Kaisei Mogami (World of Build)

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 is one of the main antagonists of Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Riders alongside his doppelgänger. He was a former researcher of the Touto Institute of Advanced Matter Physics who transformed into , also known as .
==History==
===Background===
Kaisei Mogami was a researcher of Touto Institute of Advanced Matter Physics who specialized in the study of parallel worlds. He discovered the Bugster Virus in the Sky Wall and theorized that it came from another world, leading him to develop a cross-dimensional machine called Enigma alongside Takumi Katsuragi. Although the government could not fund his project, Mogami transferred to Namba Heavy Industries Ltd. and developed Enigma. With Katsuragi as an assistant, they created the Kaiser system by infusing the Bugster Virus with the Nebula Gas.
Takumi Katsuragi would discover Kaisei Mogami's true intentions. Enigma was not built to solely transit between Build and Ex-Aid's worlds, but rather to combine and inevitably destroy them. Mogami knew this fact, yet he was hell bent on doing so since his survival was guaranteed. Realizing Mogami's true goals, Katsuragi sabotaged the Kaiser system which ended up incapacitating the left side of Mogami's body and scarring the left side of his face.
===Kamen Rider Heisei Generations FINAL===
Two years later, Kaisei Mogami would finally complete Engima and unleash the Nebula Bugsters from his native world. Under the guise of Kaiser, he intercepted Kamen Rider Build for the Doctor and Game Fullbottles. When Kamen Rider Cross-Z chased after him, Kaiser threw him into the Enigma's portal as it began activating, sending him to Ex-Aid's world. The Kaiser attempted to recover the Fullbottles but was stopped by Build and had to leave once his system developed a fault.
Mogami would continue to work alongside with his counterpart from Ex-Aid's world to use their Engimas to assimilate their worlds towards destruction. Sento Kiryu would later find him in his lab and confronts the mad scientist, but both Mogamis would finally meet as the Engima was fully bridged both of their worlds, fusing into Bikaiser. However, Kamen Rider Build would join forces with the Kamen Riders from Ex-Aid's world to put a end to Bikaiser's megalomaniacal schemes and perishes from Build Rabbit Tank Sparkling and Ex-Aid Muteki Gamer's Rider Kicks.
===Post-mortem===
Kaisei Mogami's development with the Kaiser system would be a valuable asset with Namba Heavy Industries Ltd. as the company was able to develop new models of Bikaisers. When facing one of these models, Sento initially believed that Kaisei Mogami had returned, but learned that its true identity to be an innocent test subject who was exposed to Nebula Gas. 
The late Mogami's Kaiser System had been updated by Nariaki Utsumi on behalf of Blood Stalk and Namba Heavy Industries Ltd., and the prototype's battle with Build allowed him to finalize the new Hell Bros. Fu and Rai Washio would use the completed Nebulasteam Gun to become the Remocon Bro's and Engine Bro's.
==Personality==
He is a violent, evil scientist bent on annihilating all humans, though in comparison to his World of Ex-Aid counterpart, he is the calmer and more sadistic of the two.
==Forms==
==Equipment==
===Devices===
*Nebulasteam Gun - Transformation device and sidearm
*Blue Gear Remocon - Transformation trinket
==Behind the Scenes==
===Portrayal===
Kaisei Mogami is played by . As Kaiser and Bikaiser, his suit actor is .
===Conception===
In the script of Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Riders, Kaisei Mogami's form was dubbed the , equal to the R Kaiser.https://www.daily.co.jp/gossip/2017/12/09/0010803327.shtml
==Notes==
*According the profile that Gentoku Himuro given to Sento, Kaisei Mogami is 40 years old. However his actor Kenji Ohtsuki is 51 years old at that time.
==Appearances==
* Kamen Rider Build
** Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Riders
**Kamen Rider Build: Raising the Hazard Level ~7 Best Matches~ Next Chapter 
**Episode 23: The Phantom of the West 
**Episode 27: The Counterattack Hero 
==References==
==Navigation==
Category:Movie-exclusive Villains
Category:Foundation X
Category:Faust
Category:Build Characters
Category:Deceased
Category:Debatable Riders
Category:Build Riders