Takumi Katsuragi


 * Note: This exists as a soft redirect to avoid spoiling viewers without warning. For his current identity, click here (spoilers at your own risk).

Takumi Katsuragi (葛城 巧) was a researcher at Touto Institute of Advanced Matter Physics who was murdered by Soichi Isurugi/Evolto upon discovering his true identity. Known among his colleagues as The Devil's Scientist (悪魔の科学者), he is the infamous creator of the Build Driver, the Fullbottles, the Sclash Driver, the Sclashjellies and the Transteam system.

It is later revealed that he is in fact, still alive, under the identity of a different person who has no memory of his past.

Life
The son of teacher Kyoka Katsuragi and researcher Shinobu Katsuragi, Takumi was a brilliant prodigy and among one of the best researchers at the Touto Institute of Advanced Matter Physics. Infamously called the "Devil's Scientist", the nickname stems from his extensive notes on the Pandora Box, as well as the mysterious Nebula Gas. As part of his Project Build, he harnessed the Nebula Gas and created the Fullbottles, and the Build Driver to filter out the raw power of the bottles without the dangers of becoming Smash. . He presented the idea to Gentoku, who blatantly rejected the ideas of human experimentation, but Takumi insisted it was for the sake of science. Behind Gentoku's back, he began his experiments, only to be caught and fired by Gentoku.

However his firing was only a ploy to evade him from the law as Gentoku re-approached and scouted him to join Faust, a organization funded by Namba Heavy Industries Ltd. for the sole purpose of continuing the covert human experimentations Takumi started. He was placed as head of the research team, and was successful in creating the Smash, Transteam Gun in a matter of months.

He would later entrust Project Build's research to his mother.

World of Ex-Aid
"You know, in spite of how it may seem, I'm actually a pacifist."

- Build to Genm

In the years before his death, Takumi was chosen to work alongside Kaisei Mogami on his parallel research studies. Together they build the Enigma that would allow Takumi to to visit the World of Ex-Aid on two separate occasions as Kamen Rider Build.

First Visit
Seeking a sample of Ex-Aid's essence, Build mistakenly intercepted Kamen Rider Genm while he was fighting through the Bugster Virus hordes of Gamedeus Cronus. Switching to the GorillaMond Form to engage him, only after eliminating one of Genm's lives did Build realize that he was not Ex-Aid and promptly took his leave after identifying himself to Kuroto. . Inspired by this encounter, Kuroto created a Rider Gashat based on Build, the latest in his collection of those of the Heisei Riders, which Emu Hojo snatched from his hand and activated.

Second Visit
In next occasion, Build successfully encountered Emu and absorbed Ex-Aid's essence into a Fullbottle. This led Emu to lose the ability to transform, with Parado following Build back into his native world in an attempt to track him down and get Emu's powers back. However Parado did not return in the same area as Build, where he would spend the next two years attempting to track him down. When Parado eventually confronted Sento Kiryu, the current Build, Sento claimed to have no recollection of the event, thinking of it as a dream.

"Death"
"You had me fooled, but I'm prepared now. Now, I will stop you!"

- Katsuragi to Evolto

At some point, Katsuragi discovered the true identities of both Soichi Isurugi and Ryuga Banjo and wanted to destroy them upon learning of Blood Stalk's malicious goals. Formulating a plan so that Ryuga would come by, Katsuragi confronted Blood Stalk saying he plans on leaving Faust and would never obey Evolto's orders or reveal the location of the Evol-Driver. He attempted to transform into Build GorillaMond, however his Build Driver was switched out, resulting in his Gorilla FullBottle revert back to an Empty FullBottle, rendering him unable to Transform. Evolto then knocked Katsuragi out on the spot. Ironically, Taro Satou just so happened to have arrived and get frightened by Stalk appearance, only for the latter to kill Taro, and switching their faces and clothing. One hour later, Ryuga Banjo would arrive following Katsuragi's plan (although it had already failed by the time he arrived) and be framed as Katsuragi's murderer, thus he was sent to prison.

Legacy
Shingo Kuwata has exclaimed to Build that Takumi Katsuragi is, in fact, still alive.

He had been accused of being the true identity of Blood Stalk, which was later proven false.

It is later revealed that he is still alive as Sento Kiryu, with the dead "Takumi" actually being a man named Taro Satou.

Making his debut as Kamen Rider Rogue, Gentoku Himuro addressed Sento as Katsuragi.

After the revelation that Takumi's father Shinobu Katsuragi was the one who experimented on Ryuga Banjo as a child, the truth came back to haunt Sento Kiryu.

After Sento was released by Evolto, he regained the memories of his former identity while losing those of his current one. As Takumi awoke to Ryuga Banjo standing over him, he revealed his identity to him. .

Personality
As a researcher, Takumi has no qualms going to any lengths to complete his research, even going so far as to use brutal methods such as human experimentation. Takumi himself claimed that he'll gladly sell his soul to devil, as long as science evolves even further. However, he is shown to still have a filial side towards his mother, although he does not seem to express it on the outside.

He also claims to be a pacifist when he was battling Genm, though this has yet to be proven, or at least the reasons behind his claim.

Eventually, it was revealed that his commitment to Faust's goals eventually wavered enough for Blood Stalk to consider him a traitor, and orchestrated the events that lead to his new identity and him gathering Fullbottles.

Devices

 * Build Driver - Transformation device.
 * Fullbottles - Transformation trinkets.
 * Fullbottle Holder - Carrier strap for Build's Fullbottles
 * Hazard Trigger - Build's power up device, used to upgrade into a Hazard Form by attaching it to the Build Driver.

Weapons
Handheld weapons:
 * Fullbottle Buster - Build's personal sword-like and pump-action shotgun-like weapon, accessed by any form that uses the FullFull RabbitTank Bottle.

Suit-equipped weapons:
 * Rabbit Foot Shoes - Build's rabbit-like spring shoe accessed by any form that uses the Rabbit Fullbottle.
 * Tank Roller Shoes - Build's tank-like tread shoe accessed by any form that uses the Tank Fullbottle.
 * Muscle Glove - Build's gorilla-like gauntlet accessed by any form that uses the Gorilla Fullbottle.
 * BLD Prism Glove - Build's diamond-like glove accessed by any form that uses the Diamond Fullbottle.

Portrayal
Takumi Katsuragi is portrayed by Yukiaki Kiyama (木山 廉彬). In Kamen Rider Ex-Aid media he was voiced by Atsuhiro Inukai (犬飼 貴丈) who plays his current identity Sento Kiryu. As Kamen Rider Build, his suit actor is Yuya Nawata (縄田 雄哉) in his televised debut in the 44th episode of Kamen Rider Ex-Aid.