List of Kamen Rider Build characters
Nascita. Several characters gather at Nascita, a café owned by Sōichi Isurugi where he lives with his daughter Misora. Sento Kiryu. is a 26-year-old genius who is trustful and puts the safety of others above himself. Though level-headed and compassionate, Sento is egotistical with a dangerous temper when provoked. Prior to the start of the series, he was found by Sōichi Isurugi with total amnesia except for being experimented upon by Night Rogue. Sōichi gave Sento his name and convinced him to help fight the Faust organization and its Smash creations  in hope of regaining his memories. While helping Ryuga clear his name, Sento learns that an Evolto-possessed Sōichi masterminded the events that ruined both his and Ryuga's lives, and a defeated Gentoku reveals Sento's true identity. During the events of "Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider", Sento and Ryuga encounter some Bugsters in their world, fighting despite seeing their attacks don't work, Sento decides to use Ex-Aid's powers, seeing which have an effect, Kaiser is suddenly attacked and steals the bottles Sento recovers while Ryuga is thrown into a  machine which sends him to a parallel world where the Skywall does not exist. Afterward, Sento meets Parad, who demands the Ex-Aid Fullbottles, where Sōichi appears and explains about Kaiser's, Sento and Parad decide to learn more about their plans. In the end, Sento, along with Emu and the other main Kamen Riders, decides to end the Kaiser duo's plan. Sento was actually Faust's founder, Takumi Katsuragi, whose memories were lost after a failed assassination attempt on Evolto. After being knocked unconscious by Evolto, his face was swapped with the recently murdered musician , to be experimented  upon by Gentoku as part of Evolto's plan to complete Takumi's Rider Systems for the civil war Evolto causes. However, Sento joins forces with Kazumi and Gentoku to fight against Evolto. After a failed suicide attack on Evolto, Katsuragi's personality re-emerges. Eventually, Sento and Katsuragi formed a compromise, allowing the former to regain control of his body while the other acted as his spiritual adviser. Following Evolto's destruction and apparent removal from Earth, Sento learned that "Prime" Kamen Rider universe with the Skywall Disaster has merged with their world and subsequent deaths averted. This left  Sento felt as a total stranger. He later finds his own reality's Ryuga, who was in the same situation, and the two decide to start their lives anew. It is later revealed that many of the previous episodes' opening recaps are actually memoirs written by Sento which he intends to use as the basis of a television series he and Ryuga are collaborating on, subtly breaking the fourth wall. During the "Build New World" films, Sento is convinced that Kamen Riders are no longer needed before changing his mind after Killbus appears on Earth. He later enlists Takumi's  help to develop a serum that would restore the memories and abilities of himself and his fellow Kamen Riders from their universe. Sento is able to transform into Kamen Rider Build by using the belt to combine two . Depending on the combination of Fullbottles, one of which corresponds to a person or animal and one which corresponds to an object, he can access various forms. Certain combinations work better than others, with strong forms called a . By himself, Sento's initial Hazard Level is 3 (see Smash, below). The continuous use of the Hazard Trigger and Pandora Panel (later Genius  Fullbottle) allows it to rise rapidly towards 7, allowing him to transform the Rabbit Fullbottle into a golden state. Best Matches: Build's main weapon is the , which can interchange between and . His personal motorcycle is the , which he can access by inserting the Lion Fullbottle into the . Sento Kiryu is portrayed by , who also portrays Tarō Satō. Ryuga Banjo. is a 23-year-old former professional fighter who was born in Yokohama. Prior to his birth, a portion of Evolto's essence, which had come to Earth via a Martian probe, fused with the unborn Ryuga in a failed  attempt to possess his mother at the probe exhibit. As a result, Ryuga was born after only two months of gestation, and spent much of his childhood being tested by Namba Industries. Ryuga was orphaned at age 13 when his parents died in a traffic accident, and it was revealed in "Build New World: Kamen Rider Cross-Z" that Evolto actually murdered them to raise their son's Hazard Level. Takumi Katsuragi, the founder of Faust, learned of Ryuga's nature and hired him under false pretenses, intending to kill both Sōichi Isurugi into Ryuga while they were possessed by  Evolto. Takumi's plan backfires, and Ryuga is framed for Takumi's apparent death. Ryuga was kidnapped from prison by Faust's agent Nabeshima for experimentation. Due to his half-alien physiology, Ryuga manages to escape and is found by Sento who hopes to learn of his past. Shortly after, Ryuga is forced to watch his girlfriend Kasumi Ogura be turned into a Smash, dying due to her low Hazard Level. Sento gave him the Dragon Fullbottle containing her Smash essence as a keepsake, and later a small robotic dragon-like companion known as the h. Ryuga is given a  copy of the Build Driver from Sento, and adopted the mantle of . During the events of "Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider", Ryuga and Sento encounter some Bugsters in their world, after that Sento is attacked and Ryuga continues to be transported by him in parallel world where the Skywall does not exist, where he meets Emu and his friends, along with Emu decides to find out the plans of Reverse Kaiser, and thus put an end to the plans of the Kaisers. Ryuga learned of his true origins from Vernage while manipulated by Evolto 's machinations to strengthen his alien genes to make him a more-suitable host. During the events of the film "Be the One", manipulated by Kengo Inō to attack Sento, Ryuga played a role in Sento's ability to assume Cross-Z Build Form when they absorbed him to defeat Kamen Rider Blood. In the final clash against Evolto, Ryuga sacrifices himself to restrain a weakened Evolto as they are sucked into a wormhole created by the complete Pandora Box, with Evolto absorbing him in a final attempt to survive. Sento frees Ryuga as the alien is permanently destroyed. Due  to Sento's actions, the Pandora Box transports Ryuga into the "Prime" Kamen Rider universe after it absorbed his reality. Sento finds him after running into the prime universe's Ryuga, an active sports fighter in a relationship with his reality's Kasumi. Ryuga then joins Sento in making a new life for themselves. In "Build New World: Kamen Rider Cross-Z", Ryuga lives with Sento and makes a living selling Sento's experiments, until he meets Yui Mabuchi and joins forces with Evolto to defeat Killbus, starting a new relationship with Yui in the process. In "Build New World : Kamen Rider Grease", he is in charge of delivering the Perfect Kingdom to Kazumi once Sento finishes creating it, so that he can defeat Keiji once and for all, in addition to saving Misora. Due to Ryuga's alien origins and the experiments done on him by Faust, he has extraordinary abilities such as increased strength, being able to raise his Hazard Level faster than usual and manipulating the Pandora Box. Once reaching Hazard Level 7, Ryuga transformed the Dragon Fullbottle into the Silver Dragon Fullbottle. Although a strong fighter, Ryuga is easily provoked and not too intelligent. However, he  was kind-hearted and generally puts others before himself. During Evolto's awakening of Phase 4, Cross-Z suffers from uncontrollable rage of his past life as Evolto, which also granted him the power of manipulating black holes at a smaller rate before they were ultimately neutralized when Vernage's essence was transferred into him during Misora's rescue. Ryuga Banjo has some bad qualities, for example, him dealing with his dead fiancé feeling like a rushed version of Hiiro Kagami/Kamen Rider Brave's entire arc throughout his show. His backstory revolving around him being part-alien was also  a very weird addition to his character. Additional forms: Ryuga Banjo is portrayed by . Misora Isurugi. is Sōichi's 19-year-old daughter who works as Sento's assistant. She gained supernatural power after being exposed to the Pandora Box and spending seven years in a coma. She played a role in Project Build, as Evolto used Sōichi's memories of her drawings of organic and inorganic-based objects to influence Shinobu in developing the Best Match aspect of the technology. She was kidnapped by Faust for experimentation, but Sōichi rescued her a year ago. Fearing that Faust is still  hunting her, she remained in Nascita while using her online idol identity to gather Smash intel and occasionally money from her fanbase. Misora was unaware that her father is actually a high-ranking Faust agent who used her, Sento and Ryuga as tools to create a Kamen Rider army within Touto, though she may have learned of this while being driven to despair. She later uses her powers to cure Taizan Himuro of Sōichi's poison so he can resume his duties as Touto's prime minister and thereafter discovers that her father is possessed by Evolto, the true villain  committing the crimes. During the events of "Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider", Misora is in charge of purifying the Ex-Aid bottle in two, she also helps Sento find out Kaiser's hiding place. Misora Isurugi (石動 美空, "Isurugi Misora") works with Sento Kiryu by using her ability to purify Fullbottles. Often secluding herself in nascita's basement, she is more well-known as the online idol Mii-tan (みーたん, "Mītan"), using her huge following of fans to help her seek out and collect information. She later uses the CD Fullbottle to briefly become  the CD Lost Smash (CDロストスマッシュ, "Shī Dī Rosuto Sumasshu"). Misora possesses the ability to purify and enhance Nebula Gas which made her a target of Faust. Initially, using the ability put her to sleep for a week; Sento later developed a machine to mitigate this. After she is nearly killed by a berserk Build Hazard Form, her ability increases so she can purify the higher Nebula Gas concentrations like those from the Hazard Trigger. Sento used her power to create the Fully Shook Rabbit Tank Bottle and Fullbottle Buster to negate the Hazard Trigger's side-effects. During the invasion  by Seito, the western part of Japan, Misora's Martian bracelet is revealed to house the spirit of the Martian Vernage and the source of Misora's power. Misora was later kidnapped by Evolto and turned into the that can throw discs. Sento saves her by extracting Vernage to render Misora completely human and transfers the alien into Ryuga. After the universes are merged at the conclusion of the series, an alternate Misora is shown to be a waitress at her father's café. In "Build New World: Kamen Rider Cross-Z" she recovers the memories of her alternate self  after Killbus began the process of destruction with the Pandora Box. In "Build New World: Kamen Rider Grease" she runs Piccolo Nascita, a mobile café. Misora Isurugi is portrayed by . As a child, Misora is portrayed by . Sawa Takigawa. is a 27-year-old freelance journalist dedicated to learning about Build and the Smash. Build saved her from the Needle Smash, and she assists Sento after learning his true identity. While she is a spy for Namba Heavy Industries, Sawa is actually using her position to investigate the cover-up of an industrial accident she believes killed her father. When  Misora exposed her duplicity, Sawa is punished by being turned into the octopus-themed before she is defeated by Ryuga with Sento extracting the Nebula Gas from her system. She then decides to atone for her actions and join forces with Sento's group to fight against Namba and Faust. Sawa becomes protective of Misora, especially after learning of the younger woman's past. During the events of "Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider", Sawa helps Sento find out about Kaiser's past. Sawa is later revealed to be a brainwashed Namba agent, her motivating  drive about her father being a fabrication. She was supposed to let herself die after failing Namba's mission but the familial bonds she made with Sento and the others gave her a reason to live and influenced her decision to cut ties with Namba. Sawa accomplishes this by aiding Sento in the ploy to trick Namba by giving him a fragment of Sento's research on the Fully Shook Rabbit Tank Bottle; Kazumi rescues the Nabeshima family whom Namba held hostage as leverage against Sawa, freeing her from Namba's control. She later helps take care of Sōichi, who  had entered a coma after Evolto releases him from his control. After Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Sawa is shown to also be working as a journalist. In "Build New World: Kamen Rider Cross-Z" she recovers the memories of her alternate self after Killbus began the process of destruction with the Pandora Box. Sawa Takigawa is portrayed by . Sōichi Isurugi. is the enigmatic 48-year-old owner of Nascita and Misora's father who is actually Faust's high-ranking member . He is a kind-hearted man and a good  friend to Takumi's father Shinobu Katsuragi. Ten years prior to the series, he was the astronaut who discovered the abandoned Evol-Driver and the Pandora Box on Mars. This resulted in his possession by the alien entity Evolto who used him to commit numerous atrocities including the Skywall Disaster, framing Shinobu, and manipulating Takumi and Misora for his own ends. Sōichi's personality occasionally resurfaces to briefly fight Evolto before being suppressed. Sōichi was tricked into thinking that Evolto would leave his body upon retrieving the Evol-Driver, ending up in a coma; in the meantime Evolto possessed Ryūga  then Sento before creating his own body in Sōichi's image. After Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Sōichi is shown as an ordinary café-owner of Nascita. Due to being possessed by Evolto, Sōichi gains several inhuman abilities. He can transmute matter, as shown when he transformed his tablet computer into pieces of paper. He can reshape a person's face and manipulate their memories. He can quickly leap into the air to escape. When Evolto possessed him, Sōichi uses the Fullbottle to transform into Blood Stalk. As Blood Stalk, he  can poison his opponents by stabbing them with an appendage, and hack Touto's Guardians with a simple flick. Through his animal motif, he can summon a projection of a large cobra for various applications. With the Devil Steam, he is able to either release Nebula Gas to change regular people into Smash via the Steam Blade or inject a Smash with a Nebula Gas-filled bullet to enlarge them into giants via the Steam Rifle. By using the Rocket Fullbottle, Stalk can launch guided energy missiles. Sōichi Isurugi is portrayed by . Sawatari Farm. is the Sawatari family's potato  farm in Hokuto, the northern region of Japan isolated by the Skywall Disaster. Kazumi Sawatari. is a 29-year-old soldier from Hokuto and the current owner of his farm. In hopes of obtaining more financial support, Kazumi volunteered for Hokuto's military and underwent Faust's human experimentation. Lying about his memory loss, Kazumi continued to use the Sclash Driver, which turned him into a bloodthirsty fighter, though he was able to control this effect. However, he despises cruelty; he threatened Hokuto's prime minister for ordering troops to target civilians during their invasion of Touto. He cares for  his co-workers' welfare and was visibly upset when the Hokuto Three Crows underwent additional Nebula Gas infusion, knowing that their next defeat would guarantee their deaths. He is a fan of Misora, having watched her performances alongside his co-workers. Having first infiltrated Touto during the events of "Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider" to reclaim the Phoenix and Robot Fullbottles for Hokuto, Kazumi is deployed to lead the Hokuto army to invade Touto. His alter-ego, , was created based on the Robot Fullbottle. The invasion ends with Grease defeated by Build Hawk Gatling  Hazard, and Cross-Z Charge saving Grease when Sento's Hazard Trigger goes berserk. During Seito's attack on Hokuto and Touto, he joins forces with those from Nascita in hopes of reclaiming his country. The Three Crows are killed and he gradually comes to terms with the loss, making peace with Sento and Gentoku. In hopes of catching up with Build and Cross-Z's growth in power, Kazumi and Gentoku allowed themselves to be kidnapped to forcefully raise their Hazard Levels at the risk of their lives. Kazumi fought alongside the Touto Riders to stop Evolto's genocidal  plans. During that time, Sento created the Blizzard Knuckle for Grease, but made it incompatible with Sclash Driver, which might have been fatal. When facing powerful replicas of the Three Crows which Evolto created as his enforcers, Kazumi uses the Blizzard Knuckle in Shinobu's Build Driver to destroy the copies at the cost of his life, dissipating in Misora's arms. After Sento merged the worlds at the end of the series, an alternate Hokuto Three Crows try to set Kazumi on a blind date with Misora at Nascita. In "Build New World: Kamen Rider Cross-Z" he recovers  the memories of his alternate self along with the power to transform into Grease after Killbus began the process of destruction with the Pandora Box, helping Ryuga in his fight against Killbus. In "Build New World: Kamen Rider Grease", he and the Hokuto Three Crows are the only ones who did not lose their powers because they bathed in a special water that was left of the old world, which is why only Kazumi could defeat Keiji and Downfall and thus save Misora, which he accomplishes after becoming Grease Perfect Kingdom. By himself, the injection of Nebula Gas allows Kazumi  to utilize a Fullbottle's power at a smaller rate, which was enough to incinerate a Hazard Smash. He has the following forms: Kazumi Sawatari is portrayed by . Hokuto Three Crows. The are a group of Hokuto soldiers who were originally workers of the Sawatari farm who enlisted to repay a debt to their former employer. Using Shinobu Katsuragi's Lost Fullbottles, they are each able to transform into enhanced form of the Smash known as and later the stronger , which gave increased strength but kills the user if they are knocked out of a transformation. Following their deaths, Grease  kept their Bottles as memorabilia and had once combined their energies to perform a stronger attack. Evolto later creates corrupted copies of them to serve as his enforcers. When Sento fuses the two worlds, an alternate Hokuto Three Crows are seen entering the cafeteria Nascita together with Kazumi. In "Build New World: Kamen Rider Cross-Z", they recover the memories of their alternate selves along with the power to transform into Smash after Killbus began the process of destruction with the Pandora Box. During the events of "Kamen Rider Build NEW WORLD: Kamen Rider Grease", they sacrificed their powers and  seemingly their lives to ensure Grease can transform into his Perfect Kingdom Form, but are later revealed to have survived, pretending to have died in order to give Kazumi the push he needed to defeat Keiji Uraga. Akaba. , real name , uses the Fullbottle to transform into the . He seems to possess a violent streak when he attacks civilians without hesitation, but is ultimately loyal to Kazumi, following his decisions even when he questions them. When Seito invaded Touto to steal the Pandora Box, Akaba sacrificed his life to protect it from Gentoku, but ultimately failed to prevent the theft. Akaba  is portrayed by . Aoba. , real name , uses the Fullbottle to transform into the stag beetle-themed . Despite his looks and mannerisms, Aoba is one of the kinder members of the Three Crows. He is unexpectedly killed during battle when Build goes on a rampage and uses the Hazard Finish against him. Aoba is portrayed by . Kiba. , real name , uses the Fullbottle to transform into the . He behaves childishly, even acting literally like a child throwing a fit when defeated by Build in one battle. After Aoba's death, he becomes bitter and increasingly violent in combat. While trying to defend  his homeland from Seito's invasion, Kiba becomes the Washio Brothers' hostage to force Kazumi into serving Seito. Kiba is killed protecting Kazumi. Kiba is portrayed by . Faust. is a mysterious terrorist organization that experiment on humans to create the Smash creatures. It was founded by Touto scientists Takumi Katsuragi and Gentoku Himuro. According to Gentoku, Faust's objectives are to achieve Takumi's goals of evolving humanity into the "ultimate lifeform". The organization was compromised by Evolto and Namba who sought to reassemble the Pandora Box and repeat the calamity that destroyed the ancient Martian civilization. Gentoku Himuro. is  the 35-year-old special advisor to his father, Prime Minister Taizan Himuro, and head of the Touto Institute. Initially a kind, friendly and laid-back eccentric, radiation from the Skywall Disaster transformed him into a sadistic and paranoid power-hungry maniac, who performed questionable acts for Touto's safety after deeming his father's pacifism a liability. Gentoku orchestrated Takumi's expulsion from Touto Institute to cover for the Devil's Scientist while unknowingly being manipulated by Sōichi Isurugi (and by extension, Evolto and Namba). After taking his late friend's position as the prime minister's advisor, Gentoku  took the mantle of Night Rogue and declared his leadership over Faust. During the events of "Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider", Gentoku helps Sento find out about Kaiser's past. Gentoku took advantage of Sento and Ryuga to gather more Fullbottles, perfecting most of Takumi's Rider Systems and reclaiming the Pandora Box. Gentoku was elevated to prime minister after Stalk incapacitated his father and forced the two Kamen Riders to be inducted into Touto's military. After sending Cross-Z Charge to invade Hokuto, he was dismissed by Taizan and sentenced to exile . This forced him to seek refuge at Namba Heavy Industries and served Seito's military as Kamen Rider Rogue. The experiment Gentoku received to raise his Hazard Level rendered him a near-emotionless nihilist with a restraining chip to ensure obedience, while reversing the negative effects from the Skywall radiation. Although working under Namba, Gentoku secretly assisted the Riders. During an operation to rescue Taizan, Sento deactivated the restraining chip, allowing Gentoku to return at the cost of Evolto regaining his power as Kamen Rider Evol. After Taizan sacrifices himself to save Gentoku, Gentoku begins to seek redemption by allying  himself with the Riders against Evolto and Namba, and begins to atone his past actions while reverting to his true personality. Gentoku's initial Hazard Level is 3, raised to 4 by Namba Heavy Industries experimentation so that he can use the Sclash Driver. In hopes of matching the growth of Build and Cross-Z, both Kazumi and Gentoku allowed themselves to be captured and heavily dosed with Nebula Gas to further raise their Hazard Levels. As the battle against Evolto reaches the climax, Gentoku is distraught when Utsumi sacrifices himself and Kazumi falls in battle. He ultimately dies protecting  the others during a clash with Evolto, successfully landing a critical blow on the alien. When the universes are merged at the conclusion of the series, an alternate Gentoku is working as a personal aide to his father, with a shy but polite attitude towards his world's version of Sawa. In "Build New World: Kamen Rider Cross-Z" he recovers the memories of his alternate self and the power to transform into Rogue after Killbus began the process of destruction with the Pandora Box, helping Ryuga in his fight against Killbus. In "Build New World: Kamen Rider Grease" he  tries to stop Downfall, but because his powers are stolen, he fails and is kidnapped but is later released thanks to Sawa after that Downfall is defeated, he tells Sento and Ryuga that he is dating Sawa. Gentoku's forms are accessed through the Transteam system and/or Sclash Driver: Gentoku Himuro is portrayed by . Evolto. is the true antagonist of the series and leader of both the Blood Tribe and Faust. A genocidal sociopath, prior to the series, Evolto has taken the Pandora Box away and escaped from his brother, Killbus who was using Pandora Box to destroy his home  planet. After the destruction of his planet, he used the power of the Pandora Box to destroy planets to absorb their energies as a means of gaining power and travelling. Until he destroyed the Martian civilization, he was rendered incorporeal and lost his true physical form before Vernage sealed him alongside his damaged Evol-Trigger within the Pandora Box. When a Mars rover arrived for observation, Evolto used it to send a piece of himself to Earth to acquire a host to restore himself. But it backfired when the fragment's attempt of possessing Namba Industries security guard Yuri Banjo  resulted in it being assimilated into her unborn child Ryuga. 13 years later, Evolto possessed the astronaut Sōichi Isurugi when he retrieved the Pandora Box from Mars and attempted to destroy Earth, only for Vernage's intervention to result in the Skywall Incident to scatter the Pandora Box across Japan. This forces Evolto to execute a decade-long plan of manipulating various individuals and events, such as the foundation of Faust, positioning himself within Namba Heavy Industries and grooming Ryuga as his next vessel. Evolto also used Sōichi's connections to force Shinobu and his son into working for him , tricking a young Misora to purify Fullbottles, and framed Ryūga for Tarō's death while an unconscious Katsuragi was spirited away with his memory and face altered. With Katsuragi's new identity as "Sento Kiryu", Evolto further manipulated him into perfecting the Build System and created other Rider Systems that Katsuragi purposely scrapped. In the hopes of hiding his presence, he made his original voice the default setting of Blood Stalk's system during transformation. After all Fullbottles were purified, Evolto exposed his treachery to the crews of Nascita and his plans to use the Pandora Box to destroy Earth 's civilizations, exploiting Namba as they engineered a series of schemes to take over Japan with only Touto and its Kamen Riders as their opposition. After regaining the Evol-Driver, Evolto abandoned his host to become as he transferred himself to Ryūga's body to regain his full power and then into Sento to use his intelligence to repair the Evol-Trigger. Once the Evol-Trigger was repaired, Evolto left Sento's body and became a corporeal shapeshifter, assuming Sōichi's appearance. Evolto then proceeded to kill Namba who refused to accept being a puppet ruler while winning the maddened  Utsumi to his cause. Evolto decided to take over Earth instead of destroying it after finding amusement in Namba's final moments and Utsumi's descent into insanity. Initially limited to feeling either delight or irritation, Evolto developed human emotions as a result of his Hazard Level increasing. Evolto also assumed Midō's identity to place the Blood Tribe as governors to execute Build Annihilation Plan, but a mutiny by Inō forced him into an alliance with his own adversaries. When later defeated by the four Kamen Riders using a coordinated attack, Evolto imparts a fragment of himself within Utsumi  to reconstitute himself. He then kills Shinobu while reclaiming his Evol-Driver and regaining his full strength, before splitting off a part of himself to possess Kazumi to steal back the CD Lost Fullbottle for the . He then absorbs the panel to assume his true monstrous form, but was forced back to his Rider Form by the four Kamen Riders and loses a Lost Fullbottle as well, though he escapes. Combined with his inability to emotionally compose himself, Evolto became very disappointed by the defeat and falls back to his original plan of destroying all life on Earth. As the  final battle between Evolto and the Riders began, he succeeds in causing Kazumi's death and kills Utsumi after the latter reveals his true allegiance. Evolto becomes omnipotent but Gentoku wounds him enough for Ryūga to sacrifice himself to trap Evolto in the vortex of a wormhole created by the complete Pandora Box. Evolto attempts to cheat death by absorbing Ryuga but Sento saves his friend, with Evolto seemingly erased as a side-effect of Pandora Box merging their universe with the prime Kamen Rider universe. However, Evolto reconstitutes himself through a fragment of himself that slipped into Ryuga. When  Killbus reappears again in the new world and threatens to destroy the entire universe, Evolto gracefully joins forces with Ryūga to defeat Killbus before leaving Earth to regain his full strength and body. A cruel, fierce, and ruthless character, Evolto committed several heinous acts using Sōichi's body as a vessel, killing without hesitation and on one occasion turned a child into a Smash, with his plots and actions resulting in several deaths. Evolto is a very patient manipulator, having spent years establishing his plans while winning allies or placing enemies in situations that play to his advantage, but can  be taken off guard by unexpected occurrences where he was forced to improvise. Due to the successful nature of his plots in the first half of the series, Evolto becomes arrogant and overconfident, but his reliance on luck backfired several times. It also extends to his tendency of toying with his opponents as he fails to expect a stronger counterattack, which proves costly when the Riders were able to force him out of his true form just moments after he had regained it. Another flaw Evolto suffered was his inability to handle human emotions as the result of having used  multiple host bodies and his exposure to Build, making him prone to blind rage and later expressing fear when sucked into the wormhole and facing his impending doom. In the new world, while still resentful toward the Kamen Riders and humanity, Evolto admits to having developed a new-found respect for them as he mocked Killbus for underestimating humans right before the latter is finished off by Cross-Z Evol. As Kamen Rider Evol, Evolto uses the belt and , from which the Build System was reversed engineered. As a Rider, he possesses high-speed movements on par with any previous  Kamen Riders, matched only by Build Genius Form. Each of his forms are treated as an evolution of his : Evolto is voiced by . While possessing Sōichi Isurugi and later assuming his likeness, he is played by Yasuyuki Maekawa. Faust agents. Masahiro Nabeshima. is a prison guard who frames Ryuga Banjo for the death of Touto Institute researcher Takumi Katsuragi, then delivers Ryūga to Faust for experimentation. After luring Sento and Ryuga to Seito, he was converted into Mirage Smash as a "reward" and later into Square Smash as part of Blood Stalk's experiment. Although rescued by Build and Ryuga , the experiments erased almost all of his memories. Sometime later, he regained his memories and revealed information about Faust to Sento, including Blood Stalk's identity. He and his family later are captured by Namba and used to force Sawa to betray her friends. Masahiro Nabeshima is portrayed by . Eita Kawai. is a researcher in the Touto Institute and one of Katsuragi's sympathizers. He uploaded data of Pandora Box before the Faust army stole it. Blood Stalk transformed him into the to fight Ryuga Banjo, but he was easily defeated. A weakened Kawai was reverted to his human form  by Stalk, who erased his memories and altered his face to look like Kuwata. Eita Kawai is portrayed by . Shingo Kuwata. is a Touto Institute researcher and a Katsuragi sympathizer. He uses his Fullbottle to become a version of the Flying Smash. After being defeated by Build, he reveals that he was meant to lure Build away from Faust's raid to steal the Pandora Box. Before committing suicide, he reveals that Takumi had been faking his death. Shingo Kuwata is portrayed by . Guardians. The are enforcement androids mass-produced by Namba Industries as peacekeepers of each country, though it  is not initially known that they are supporting governments outside Touto. They also act as Faust sleeper agents awaiting activation by Blood Stalk. They are armed with the and ride motorcycles called . A large number of them can combine together to form a single gigantic robot equipped with multiple guns. Under Faust's servitude, the reprogrammed Guardians can act as suicide bombers. Smash. The are monsters formed by humans injected with the liquefied as part of Faust's experiments. The experimental subject loses almost all of their memories. To revert a Smash back to a normal human, the Kamen Riders  must defeat them and extract their element liquids into an Empty Bottle (which can later be purified into a Fullbottle for their transformation and equipment uses). Faust agents are given their own Fullbottles to transform into their Smash forms, which are equipped with a self-destruct function. Silver-colored Smash are stronger versions, achieved through exposure to Nebula Gas of higher Hazard Levels. The experiment's goal was to find a perfect candidate for the Build Driver, with the Smash transformations considered failures. Each victim is ranked by their tolerance of Nebula Gas called . The Smash monsters include: Enhanced Smash  (Hazards): Clone Smash. The , unlike regular Smash, are created from pure Nebula Gas, and attack until destroyed. Being enhanced versions of the Press, Stretch, Strong and Flying Smash Hazard, the Clone Smash are stronger and more durable due to their inability to feel pain. The Clone Smash are later used as materials to power a Lost Fullbottle to enable its user's transformation into a Lost Smash. Lost Smash. are Smash breeds created by Evolto and Katsuragi as the final Smash evolution. The experiment includes a human victim being heavily dosed with Nebula Gas and transformed into the Lost Smash  by absorbing a pair of nearby Clone Smash. Aside from heightened aggression and being easy to manipulate, they are also bound to die should they be defeated. The Genius Fullbottle of Kamen Rider Build has the ability to save these victims and remove traces of Nebula Gas. The Lost Fullbottles created by Shinobu Katsuragi were used to invoke the target's transformation into Lost Smash. Their actual purpose is to complete the Lost Panel of Pandora Box to take control of humanity. The full set of Lost Fullbottles work differently depending on the Pandora Panels they slotted into: the Last  Pandora Panel Black allows Evolto to regain his monstrous form by absorbing it, whereas its White counterpart can merge with five other Pandora Panels to fuse Earth with its alternate counterpart and avert the Skywall Disaster. Namba Heavy Industries. is a company established by Jūzaburō Namba which provides financial support to Faust. Because of its pervasive influence, all three countries attempted to distance themselves from Namba, although the company has agents placed within the governments' infrastructures. Jūzaburō Namba. is the corrupt and war-mongering chairman of Namba. He initially collaborates with Faust and Evolto to acquire the Build system for  military applications, but has a secret agenda to use the Pandora Box's energy to create weapons of mass destruction. He also brainwashed children to act as his agents, including Sawa Takigawa. A power-hungry man with a god complex, he will do anything to attain his goals. However, he is not completely cruel as he was shown to be close to Nariaki Utsumi in flashbacks. His ultimate goal is to use the power of the Pandora Box to reform Japan, and eventually the entire world, under his rule and in his image. However, Evolto exploited him for its own  agenda. Namba then requests aid from the Kamen Riders against Evolto, but they fail and Namba is killed by Evolto while begging for his life. In the merged universe at the end of the series, an alternate Namba owns a metalworking factory known as , rather than a huge weapons manufacturer. Jūzaburō Namba is portrayed by , while Norimasa Fuke portrays Namba's disguise as Masakuni Midō. Namba Children. The are scientists, soldiers and spies who were brainwashed by Jūzaburō Namba from an early age. They are positioned as sleeper agents within Touto, Hokuto and Seito to inform for Namba while acquiring  whatever Namba needs. Nariaki Utsumi. is the 28-year-old secretary of Himuro who was formally a Touto Institute scientist. Despite his commitment to Faust, Gentoku and Namba Heavy Industries, Utsumi expresses regret over his life choices, even commenting to Sento about their similar predicaments. To conceal Faust's activities, Utsumi became a scapegoat by masquerading as Night Rogue. His attempted suicide is stopped by Sento, but Utsumi is gravely injured and converted into a cyborg by Evolto. Utsumi then returned to Namba as his spokesperson and developed the Rider Systems for Hokuto and Seito, gathering data on the Hazard  Trigger while perfecting the Kaiser System. Although he seemed to become more open-minded, Utsumi was actually a callous sadist and completely loyal to Namba. After Evolto turns on Namba and killed him, Utsumi faked losing his sanity and was recruited as Evolto's enforcer, Kamen Rider Mad Rogue, briefly serving as a host to a fragment of the alien's body. But as Evolto neared his end goal, Utsumi reveals his deception and allies himself with Gentoku to avenge Namba while destroying Evolto's replicas of the Washio Brothers. Though his cybernetics burn out as Evolto defeats him, Utsumi  sacrifices himself to shield Gentoku and Sawa from the alien's attack. After the worlds are merged at the end of the series, an alternate Utsumi is shown working in Namba's metalwork factory. In "Build New World: Kamen Rider Cross-Z", when Killbus restored the Pandora Box, Utsumi's lack of Nebula Gas administration prevented him from regaining the memories of his alternate self. But despite that, in "Build New World: Kamen Rider Grease" he recovers the memories of his alternate self along with his powers of Kamen Rider through the injection of Nebula Gas, assisting the other Riders  in their battle against Down Fall. Utsumi twice became Night Rogue as a decoy. His modification on Night Rogue grants him the ability to analyze his opponent through his visor. As the creator of the perfected Kaiser System, Utsumi is able to transform into Hell Bros using the Nebula Steam Gun. As Hell Bros, his main weapons are the Nebula Steam Gun and the Steam Blade. With the Evol-Driver Utsumi can become by using the and Fullbottles the Evol-Driver's scrambles both elements of Fullbottles into a symmetrical form and his is specially tuned for human use. As  Utsumi was planning to betray Evolto from the beginning, his Evol-Driver was modified to imitate Evolto's Phase evolution but the full power was too much for his cybernetics to handle. In a similar vein to Evolto, Mad Rogue also possesses a Rider Evol-Bottle, allowing him to manifest the power of a single Fullbottle. Nariaki Utsumi is portrayed by . As a child, Utsumi is portrayed by . Masuzawa. is a spy who works as secretary to the Touto prime minister. When he is exposed by Sento, he kills himself using a Fullbottle to avoid capture. He is responsible for  slipping a listening device into the Dragon Fullbottle to spy on Sento. Masuzawa is portrayed by . Washio Brothers. The are a pair of siblings from Seito who serve alongside Gentoku as Seito's main troopers. The indoctrination and training they received transform them into sadistic soldiers who use deception and dirty tricks to accomplish their tasks. They transform using the Kaiser System developed by Kaisei Mogami and Nariaki Utsumi, with a shared . Because of their limited supply in weaponry, the Nebula Steam Gun's Rifle Mode (combined with the Steam Blade) can only be held by one of them while  the other engages in hand-to-hand combat. After Evolto declared war against Namba Heavy Industries, the Washio Brothers form an uneasy alliance with the Riders before losing their lives. Evolto created his own copy of the Washio Brothers' Kaiser forms as guardians at the Pandora Tower. Utsumi revealed that he had sabotaged the Kaiser Systems and programmed both Same and Bike Fullbottles as countermeasures, used by Rogue and Mad Rogue to destroy the copies. Hard Guardians. The are enhanced versions of the Guardians which Namba Heavy Industries mass-produced following Seito's war declaration on Touto. When Namba Heavy  was disbanded, the remaining units were under control of Evolto and served as the front line of Pandora Tower's defense. The Hard Guardians are equipped with a combat AI unit, right arm-mounted gatling-guns, left arm-mounted clawed gauntlets, and shoulder-mounted missile pods. An improved drive module was placed on each joint to provide enhanced mobility. Their equipment can be replaced depending on the combat situation and can fight on equal terms against Rider Systems users. Katsuragi family. Takumi Katsuragi. is 26 years old and the past identity of Sento Kiryu, infamously known among his peers as  . During the Sky Disaster, unaware of the full truth at the time, Takumi promised his father Shinobu that he would stop the Blood Race from destroying the Earth and restarted where he subjected himself to Nebula Gas to become Kamen Rider Build, only to be banned for conducting unethical human experimentations with the Nebula Gas to evolve humanity. During this period, Takumi assisted his former Touto colleague Kaisei Mogami in building the Enigma system to travel to another reality. While testing the performance of Kamen Rider Build in said world, he twice intervened in the confrontation between humans and Bugster . Having accidentally killed Kamen Rider Genm prior, Build went on to extract Ex-Aid's samples into a single Fullbottle before foiling Mogami's intent to cause a convergence between the two realities and stopped him. Sometime after developing both Rider and Transteam Systems, Takumi learned that Faust had been compromised by Evolto. He halted the development of the Sclash Driver system and attempted to kill Evolto but was outsmarted. His memories and appearance were changed to Sento, and he was manipulated into completing the Rider System. Takumi regained his memories when Evolto regained his perfect form, and becomes Build  again but refuses to work with the others. When the Genius Fullbottle refused to cooperate, he was visited by Sento's consciousness and allowed this alter-ego to access Genius Form for the first time. From that point onward, Takumi served as a spiritual adviser to Sento despite his sense of pessimism. Following the worlds' convergence, as revealed in "Build New World: Kamen Rider Grease", Takumi exists as a separate being from Sento in their new universe and works despite being plagued by unpleasant memories of the old world. Alongside Sento, he creates a special serum that enables the Rider  System users to recover the ability to transform and to be immune to the Phantom Crushers' special ability. After Downfall is defeated, Takumi returns to the . As the true creator of Build's Rider System, Takumi can use the basic Best Match forms. As he was absent while Sento further developed Build, Takumi had to retool it to keep up with its performance. Takumi Katsuragi is portrayed by , whereas his cameo appearances as Build in "Kamen Rider Ex-Aid" were voiced by Atsuhiro Inukai, Sento's actor. Shinobu Katsuragi. is the father of Takumi Katsuragi and a member of the  Kiwami Project which saw Sōichi Isurugi come into contact with the Pandora Box. Shinobu conducted illegal research on an infant Ryuga. Later, Shinobu led the conference of the Pandora Box's discovery when Evolto caused the Skywall Disaster, and his reputation was ruined as he was used as a scapegoat. Shinobu faked his suicide soon after cryptically informing Takumi that Ryuga is essential to stop Evolto and his kin, enlisting Reika Kine's aid in smuggling himself out of Touto. Shinobu secretly aided Evolto for ten years by using his research in an attempt to repair the Evol-Driver before  Takumi found and hid it. Shinobu also developed a man-made variant of Fullbottles called , also referred to as for short, which allow the user to transform into a Lost Smash with side-effects of heightened aggression and suggestibility. Shinobu resurfaces while Sento and his allies are searching for the Lost Fullbottles, revealing his alliance with Evolto while alienating Sento. However, Shinobu's plan was to eliminate the alien, pretending to be Evolto's ally while creating a specialized Best Match combination that could defeat the alien. He reveals his intentions to Sento when he thought Evolto had been defeated , but Evolto recovered and fatally wounds Shinobu. Shinobu lives long enough to give Sento his data to finalize the Cross-Z Build Form and apologize for hurting him. He comes back to life and like his son, he works as a scientist in the Japan Institute of Advanced Matter Physics in the new world. In "Build New World: Kamen Rider Grease" he created a copy of the Build Driver, which was owned by the Japanese government before being stolen by Downfall. After Downfall is defeated, he apologizes to Takumi for using him in the old world. As the founder of  Rider System, Shinobu possesses his own copy of the Build Driver and a set of Fullbottles to transform into another Kamen Rider Build. While having access to Best Match forms, Shinobu is capable of outmaneuvering the strongest of his opponents in one-on-one fights though he has difficulty fighting multiple opponents. He can also use another Fullbottle's power without transitioning, such as the use of Phoenix Fullbottle as an escape while still in Rabbit Tank form. Shinobu Katsuragi is portrayed by . Kyōka Katsuragi. is Takumi's mother and Shinobu's wife who was abducted from Hokuto and transformed  by Faust into the first . She was purified by Build, with the extracted element purified to create the Lock Fullbottle, before she entrusted the flash drive that contains the information of the Project Build to Sento. Kyōka Katsuragi is portrayed by . Prime ministers. Taizan Himuro. is the 67-year-old father of Gentoku and the prime minister of , a pacifist state with only enough military strength for self-defense. Despite the rivalries, Taizan wishes for Japan to reunite. Due to his poor health, he sent his son Gentoku to the unveiling of the Pandora Box, and retained his sanity as  the only leader not affected by its radiation. Taizan suffered a heart attack during Faust's raid on Touto facility, and entrusted Gentoku as acting prime minister, unaware that Gentoku is high-ranking Faust-member Night Rogue. The Touto government was then compromised until Sento and Ryuga defeated Night Rogue, exposing his identity to Taizan who then orders his son to be taken into custody. Sōichi later poisoned Taizan which once again gives Gentoku emergency power to rule Touto. Taizan eventually recovered through Misora's power and exiled Gentoku while looking for a way to end the war with the  least bloodshed. Taizan believes there is still good in Gentoku and vows to return his son. As Namba and Stalk enact their plan to bring humanity into chaos, Taizan is kidnapped by Gentoku so Stalk can force Sento into reviving the original Project Build. Gentoku was already planning to save his father, working with the Kamen Riders against Evolto, but the plan backfires and Evolto transforms into Kamen Rider Evol. Taizan becomes the first victim of Evolto, sacrificing his life to save Gentoku from the alien. This act allows Gentoku to fully revert to his true self. Taizan Himuro is  portrayed by . Yoshiko Tajimi. is the 53-year-old prime minister of , a social welfare state which puts the needs of its people above all else. The Skywall Disaster rendered most of the farmland infertile with the resulting economic collapse forcing many citizens to take their children out of school. Tajimi's personality was affected by radiation from the Pandora Box, and she secretly directed government funds from social welfare to the military. The machinations of Sōichi, Namba and Gentoku cause war between the other two countries to take the Pandora Box by force, and she declares war on Touto . Her ruthless behavior during the invasion disgusts Kazumi as he threatens her to stop targeting innocent civilians. During Touto's fight against Hokuto, Tajimi acts on Sōichi's advice to station her entire military on Touto's border to invade if Grease was defeated. But Tajimi realized she had been manipulated into leaving her nation vulnerable to Seito, which invade and take her into custody. She is later brainwashed by Evolto, transforming her into the before being defeated and freed by Kamen Rider Build's Genius Form. This purified Tajimi's mind leaving her horrified and remorseful over everything she  had done while being the only surviving prime minister. Yoshiko Tajimi is portrayed by . Masakuni Midō. is the 61-year-old prime minister of , which seeks economic recovery through technical advancement, sending its young adults across the world to gather technical knowledge. Midō expressed an interest in Tajimi's offer for alliance, but stood by while Hokuto and Touto weakened each other in warfare. When Hokuto lost to Touto, Midō sends Seito's military to invade Hokuto, taking over the country and capturing Tajimi. However, Midō is also a nervous man as shown by his reaction during the Touto-Seito  proximity match. After losing the fight against Touto, Midō keeps his agreement with Touto while falling out with Namba, resulting in his death by Evolto. The alien then had Namba assume Midō's identity to use the country for Namba Heavy Industries' operations and his future plots. Evolto later poses as Midō during his endgame plan and places his kinsmen into governor positions. Masakuni Midō is portrayed by . Vernage. is the former queen of Mars who survived the destruction of her civilization at the cost of her physical form. She managed to seal Evolto along with his Evol-Trigger into  the Pandora Box, while separating his Evol-Driver to prevent him from using it inside the box to free himself. When the artefacts were returned to Earth, her spirit was preserved in a bracelet which latched onto a young Misora. Ten years later, Vernage's consciousness slowly awakened and occasionally rescued the Kamen Riders from Namba's forces. As her spirit resided within Misora's bracelet, she provided the young girl with the ability to purify Nebula Gas. The process caused Vernage's memories of her civilization's destruction to play within Misora's mind. Although presented as a powerful  entity, she pointed out that her life force is diminishing. Vernage left Misora's body to restore girl's humanity while she was transformed into CD Lost Smash, and transferred herself into Ryuga to counteract the psychological effects from the trace remnants of Evolto's genes. Vernage passed away after Evolto's death, having fulfilled her goals. Vernage is voiced by . Spin-off exclusive characters. Kaisei Mogami. is the main antagonist of "Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider". A cyborg, Mogami was a researcher in the Touto Institute of Advanced Matter Physics and an associate  of Takumi Katsuragi. Ten years earlier, while researching parallel universes, he found the Bugster Virus at the Skywall and concluded that the virus is from a parallel universe. He wanted to create the interdimensional gateway , but couldn't get funding so he moved to Namba Heavy Industries to continue his research. With Takumi's help, he developed both the Kaiser system and the Enigma which allowed him to make contact with the prime universe version of himself who is a Foundation X scientist. However, he lost the left side of his body due to an Enigma accident, caused by Takumi  who opposed his ultimate goal. He resurfaces to cause the fusion and destruction of the two universes with the Enigma, to fuse with his counterpart and form a single immortal entity to become the ruler of all the universes. The two Mogamis form an alliance as they employ Foundation X's version of the Guardians known as the while creating the Nebula Bugster strain. Both Mogamis eventually fuse, but their plans are foiled before being defeated by Ex-Aid and Build, the latter fulfilling their scheme to merge their dimensions months later while defeating Evolto. Mogami is able to transform  into the blue-colored , while his counterpart transforms into the red-colored . They can also combine to form a single entity known as . Utsumi managed to acquire the Kaiser System blueprints after Mogami's death and perfected the technology, which he gave to Seito as the developed Hell Bros gear used by the Washio brothers. Kaisei Mogami is portrayed by . Blood Tribe. are a mysterious race of extraterrestrial origin who originated from before it was destroyed by their ruler Killbus. Led by Killbus's younger brother Evolto, the four surviving Blood members caused the downfall of the Martian civilization and  many other planets before possessing the four astronauts sent to explore Mars. Kengo Inō. is Evolto's second-in-command who served as advisor to Seito Prime Minister Midō and influenced Sento meeting Ryuga, later becoming governor of Touto by the events of "Kamen Rider Build the Movie: Be the One", after the Japanese civil war had ended. He then leads a mutiny against Evolto to carry out the Blood Tribe's initial plan to destroy Earth, Inō using the Tokyo populace's anti-Kamen Rider sentiment to hypnotize them into hunting down Sento with an infected Ryuga made into  his personal agent. Once acquiring the Hazard Trigger to enable his transformation into Kamen Rider Blood, Inō later acquires the Pandora Box to proceed to travel down to Earth's core and destroy the planet from the inside-out. But he is destroyed by Kamen Rider Cross-Z Build. Possessing the Cobra Lost Fullbottle, Inō uses it with Ryuga's Build Driver and Great Cross-Z Dragon, combined with Sento's Hazard Trigger to transform into . The form initially requires him to absorb nearby Blood Tribesmen, including Ryuga for possessing Evolto's essence, before Build extracted the absorbed targets from  his body. Blood rivals the strength of Build's Genius Form and can summon energy cobras as reinforcements. Kengo Inō is portrayed by . Mitsuomi Gōbara. is a member of Blood Tribe and a former advisor to Hokuto Prime Minister Tajimi, having orchestrated Kasumi Ogura's conversion into a Smash, before becoming the new governor of Seito. He can transform into using the Lost Fullbottle. He was defeated by Kamen Rider Grease after initially defeating him in their first encounter. Mitsuomi Gōbara is portrayed by . Ryōka Saiga. is a female member of Blood Tribe and a former aide to Touto Prime  Minister Himuro before becoming the new governor of Hokuto. She can transform into using the Lost Fullbottle. She is defeated by Kamen Rider Rogue after initially defeating him in their second encounter. Ryōka Saiga is portrayed by . Killbus. is the older brother of Evolto and the "Build New World: Kamen Rider Cross-Z", a suicidal hedonist who ruled Planet Blood before destroying it as part of his plan to use the Pandora Box to destroy the entire universe along with himself. Using the form of a famous dancer named Satoshi Kakizaki after appearing from the , Killbus hunts Evolto within Ryūga  to restore the Pandora Box and seeks to absorb Ryuga and Evolto into the white panel to obtain enough energy to destroy the universe. He is later defeated by Ryūga in the Cross-Z Evol form. By inserting the (Sento's robotic spider-like pet converted into a transformation item by Killbus) loaded with the Fullbottle into Sento's Build Driver, Killbus transforms into . Killbus transformed into Build before adopting his personal Rider namesake. By himself, Killbus can use the Drill Crusher and Kaizoku Hassyar as his weapons and summon Hazard Smash clones. Killbus is voiced by . While assuming the  forms of Sento Kiryu and Satoshi Kakizaki, he is portrayed by Atsuhiro Inukai and Gaku Shindo, respectively. Satoshi Kakizaki. is a famous dancer whose form was copied by Killbus. While Killbus in public, Killbus was heavily mistaken for the dancer himself, leading the media to think that "Satoshi Kakizaki" had gone crazy. After Killbus' death, the current status of Kakizaki's public image was restored to normal. Satoshi Kakizaki is portrayed by . Yui Mabuchi. is a young elementary school teacher who is looking for Kamen Rider Cross-Z, because she has faint memories of what happened before Sento merged the  two worlds, when she was captured by Faust and died as a result of their Lost Fullbottle experimentation. After Killbus began the process of destruction with the Pandora Box, she recovers all the memories of her alternate self and blames Ryūga and the other Kamen Riders for not saving her together with her students, who are still in comas due to the events of the old world where they were attacked by Faust's Guardians. After Killbus is defeated and her students recover with the power of the Genius Fullbottle, she forgives Ryūga and to others, helping him in the  sale of Sento's experiments and starting a new relationship with him in the process. Yui Mabuchi is portrayed by . Downfall. is an international radical terrorist organization that appear as the antagonists of "Build New World: Kamen Rider Grease". Its members are actually those who had been experimented by the Nebula Gas and ex-Faust members from the old world; all aiming to exploit the Rider System and achieve world domination. They hack Japan's Guardians and Hard Guardians to use the androids as their weapons. Using man-made , they can transform into olive green-colored battle forms known as  ; are armed with missile launchers, aerial capabilities, and the ability to disable Rider Systems with their right hand, which can absorb the Rider System users' Nebula Gas to lead them to lose the ability to transform. Downfall is notable for being the first villain organization in the Kamen Rider series where the majority of its members are portrayed by foreigners. Keiji Uraga. is the leader of Downfall known for his face who is a mad scientist captivated by technological advancement driven by war. Like Yui Mabuchi, he has burn marks and his memories of the old world because he was  a Lost Fullbottle test subject. He was originally one of Faust's scientists who studied the Last Pandora Panel White alongside Shinobu Katsuragi and Evolto, but died as a result of their Lost Fullbottle experimentation. He determined to obtain the Last Pandora Panel White and dominate the new world as revenge for the old world that did not acknowledge his brilliance as a scientist, and he found , which is more powerful than Nebula Gas, before creating the Phantom Crushers using the liquid. He takes Shinobu's Build Driver and Sento's Hazard Trigger to become his own Build, which he  calls , to confront the Sawatari farmers. He is later defeated by Kazumi in the Grease Perfect Kingdom form. As Metal Build, he resembles the original Build Hazard Form using a pair of Fullbottles; hence his black colored eyes. Aside from retaining Build Hazard's abilities, his use of a similar Fullbottle pair negates the Hazard Trigger's side-effects. After he is weakened by Grease Blizzard, Metal Build absorbed the Last Pandora Panel White and merged with a Phantom Crusher to become ; equipping him with the Phantom Crusher's armor, which allows him to use super speed, aerial combat, missile  bombardments, and even a copy of the original Build's Drill Crusher. Keiji Uraga is portrayed by . Simon Marcus. is a high-ranking official of the Alliance of Nations who seeks to dominate the world in collaboration with Downfall. Like other Downfall members, he also transforms into a Phantom Crusher. He is later shot dead by Uraga, who no longer needs him. Simon Marcus shares his name with a real life professional kickboxer, portrayed by .