Seiichiro Matsui

, nicknamed , was Sokichi Narumi's partner in 1999 who used the Spider Gaia Memory to become the and the main antagonist of Kamen Rider Skull: Message for W.
==Personality==
When first introduced, Matsu acted in a jovial manner toward others, with Sokichi viewing him as a good friend and partner. Rather quick with his tongue, Matsu often bantered with Sokichi in their daily lives, teasing the latter for his quirks. In their cases, Matsu assisted his partner from the background, giving Sokichi the necessary data for his deductions. 
From this however, Matsu began to have an inferiority complex toward Sokichi, envying his cool personality and prowess as a private detective. Worse, subconsciously feeling that Sokichi did not truly view him as an equal, Matsu secretly felt a sense of depression, something he hid within himself. 
Upon meeting the opera singer Melissa as a client, Matsu was attracted to her, becoming bent on "outdoing" Sokichi in their given case. Rashly using the prototype Spider Memory to fulfill Melissa's request, Matsu grew more twisted with time, with his powers evolving beyond their initial capabilities. Using these newfound powers to lash out at others, Matsu attempted to abduct Melissa as his bride, no longer having any qualms as a criminal. Having devolved into a cruel monster, Matsu viciously attacked Sokichi one final time, ultimately meeting his end from Skull's finisher attack.
Being freed from his insanity, Matsu looked at Sokichi and uttered his name, dying with a sincere smile when Sokichi reaffirmed Matsu as his partner. 
==Super Hero Taisen==
The Spider Dopant was revived as part of Dai-Shocker in the Super Hero Taisen incident, led by Tsukasa Kadoya/Kamen Rider Decade, rivaling Captain Marvelous/Gokai Red and Dai-Zangyack. However, Rider Hunter Silva of Dai-Zangyack and Doctor G of Dai-Shocker overthrew their respective leaders and joined forces to destroy the Kamen Riders and Super Sentai. The two evil organizations united and faced off against the combined forces of the Sentai and Riders.
==The Fateful Sengoku Movie Battle==
to be added 
==Abilities==
As a private detective, Matsu is shown to be highly efficient at collecting data, similar to Philip when using the Gaia Library. 
As the Spider Dopant, Matsu gained the ability to use powerful threads called the Spider Web to attack and immobolize his foes. From his negative emotions synchronizing with the Spider Memory, Matsu's powers evolved beyond its initial capabilities, giving him the ability to implant small and destructive Spider Bombs into humans, with each being programmed to explode upon their hosts touching the person they love most. 
Unlike future Dopants who lived from their Memory Breaks, Matsu died from the Spider Memory's side effects after it was destroyed because Museum's Gaia Memories were still in developmental stages at that time.
==History==
Sokichi had come across Matsu one day and they became partners for solving cases that the police couldn't handle. One day Melissa came in and asked for their help. Through some means, Matsu gained the Spider Memory to become a Dopant in order to fulfill the job while also stalking her in attempts to make her love him.
Matsu would then fight his partner as the Spider Dopant and Sokichi then figures out Matsu's identity after recognizing the way Matsu writes the number "1". After Melissa explains Matsu's reasons for taking the Gaia Memory, Matsu becomes the Spider Dopant, kidnaps Melissa and implant his Spider Bombs on the people of Futo City.
Chasing his partner to a bridge as Kamen Rider Skull, Sokichi expresses his regret for not seeing Matsu's madness and stopping him sooner and they have one last fight where Skull defeats the Spider Dopant with a Rider Kick Maximum Drive and Matsu dies from the memory's side effects. Despite the heinous actions he commited as the Spider Dopant, both Sokichi and Melissa grieved Matsu's death, recognizing him to have originally been a good person. 
==Behind the Scenes==
===Portrayal===
Matsu was portrayed by .
===Concept Art===
Spider Dopant was designed by .
==Notes==
*Matsui follows a tradition of many Kamen Riders of the first kaijin opponent being a spider, due to Man Spider, the very first Kamen Rider kaijin.
**Although not the first seen Dopant in the W universe, it is the historically first Dopant and the one who made the biggest impact in a period before the actual series.
**Matsui's nickname as a criminal, "Man Spider", is the exact same name as the original kaijin.
*The Spider Dopant was the only monster seen on the Kamen Rider × Super Sentai: Super Hero Taisen trailer that was 1:30, and did not physically appeared in the movie.
*Considering the staggering number of on-screen deaths from the his bombs, Matsu as the Spider Dopant may very well have the highest kill-count among all the Dopants in Kamen Rider W, possibly surpassing the likes of Isaka Shinkuro/Weather Dopant himself. 
==Appearances==
* Kamen Rider W
**Kamen Rider × Kamen Rider OOO & W Featuring Skull: Movie War Core
** 
==External Links==
*Kamen Rider Zukan page on Seiichiro Matsui.
*Kamen Rider Zukan page on Spider Dopant.
== Navigation ==
Category:Deceased
Category:W Characters
Category:Dopants
Category:Dopant users
Category:Villains
Category:Movie-exclusive Characters
Category:Movie-exclusive Villains
Category:Spider Monsters