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 initially had no memory of his past. Takumi's memories would later resurface alongside his new identity's memories.

Early Life
Takumi Katsuragi was born to Kyoka Katsuragi and researcher Shinobu Katsuragi. In his youth, Takumi was considered a brilliant prodigy and would often mess around with his hair, as his father often said. Sometime during grade school, his father posed a question as to whenever he would join him in preventing an alien invasion should it happen, and Takumi said yes.

During the Sky Wall Disaster, Takumi was bewildered to see Shinobu be one of the main causes of it, and asked why his father did it. He said it was for "love and peace", which Takumi, later Sento Kiryu use as his main inspiration for fighting.

Takumi later received a job at the Touto Institute of Advanced Matter Physics shortly after his father's death, but was unaware that his father was actually still alive at the time. Taking up his father's research on the Project Build, Takumi was revered as one of the best researchers at the institute, and was infamously nicknamed the "Devil's Scientist", due to his extensive notes on the Pandora Box, as well as the mysterious Nebula Gas. As part of the project, he continued the development of 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 reverting 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’s 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 Sento Kiryu 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.

Shortly before the Enigma crisis, Sento recalled the memory of Katsuragi's encounter with Ex-Aid in a dream, leading him to discover the Fullbottle that Katsuragi had acquired. As yet unaware of his connection to Build's creator, Sento insisted he was the victim of mistaken identity when confronted by Parado.

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. .

Resurfacing with Takumi's memories, he is surprised that Evolto has reached his final form and watches the other Riders fight Evolto again. Shortly however, Gentoku realized that they were outpowered and forced the entire team to retreat back to nascita.

Back at nacita, Takumi is overwhelmed by his new look and continuously wonders how this was even scientifically possible. He began to scribble over his marker board while overhearing the others discussing his nickname "The Devil's Scientist", saying "devil" was uncalled for. He recognized Misora Isurugi as the girl whom he had purifying Fullbottles for while he was with Faust, all in the name of science. Takumi began to wonder why Ryuga Banjo was helping him, despite him having Evolto's DNA, and believes that even if the DNA was gone, Evolto could still awaken inside.

Takumi is called out to talk by Gentoku Himuro, and the two exchange words on how Gentoku mad misused the Rider System for war. Gentoku apologized and said the Pandora Box altered his mindset, but Takumi didn't want to hear excuses since it was undeniable that it was them both that were responsible for the war. Takumi knew that even though Gentoku wanted to use the Kamen Riders for war, he convinced himself it was solely to stop Evolto's upcoming attack, and that the sacrifices made were necessary. In the end, Takumi walks away, saying he never should have trusted Gentoku.

Later, the team enter Evolto's space of creation to help Utsumi on his request to stop Evolto. However, Takumi is unable to keep up with Build RabbitRabbit form as it was too high-performance for him. Evolto comments that Takumi will never be able to use the latest version of Build, but Takumi proclaims that he can and he will, because he built Build for the sole purpose of beating Evolto. Takumi attempts to use the Pandora Box panel, but is froze still by the electrical output of it. Evolto takes this chance to punch him back and force him out of his transformation. Evolto takes the later chance to kill both Rai Washio and Fu Washio, thus Takumi becomes angry to see lives being lost in front of him. Evolto hands Utsumi a Evol Driver and he transforms into Kamen Rider MadRogue, where he fights Gentoku. Gentoku is defeated and Grease arrives in the nick of time to help the team escape.

Back at nascita, the team pounders on what to do now that Evolto has voiced his intent to take over the country, and want to investigate why Evolto now wants to rule a planet rather than destroy it. Takumi wishes to complete the new power-up item to defeat Evolto, along with Ryuga, who is beginning to have episodes of Evolto's memories surfacing in him. Later that night, Takumi completes the Genius Bottle and is confident he can defeat Evolto and Ryuga. Misora berates him for not believing in his friends, but Takumi said friends can only lead to distrust and betrayal. The next day, Takumi hears Gentoku regretting his actions in the past and wants to make it up and asks the team to believe in him.

Takumi heads out to "help" Cross-Z and Grease with RabbitRabbit Form, now modified to fit his specs, and easily defeats the Clone Smash. He fights MadRogue to an equal standstill, but is knocked back when Utsumi questions his motives for science. Takumi reveals the Genius Bottle and tries to use it, but it wouldn't activate. Theoretically, he should be able to use it, but Takumi didn't know why he couldn't, as MadRogue attacks him and forces him out of his transformation. Ryuga arrives to fight MadRogue and tells Takumi that he lacked heart and compassion. Sento on the other hand, fought for justice and was the epitome of a superhero, traits that Takumi didn't have and lacked with over the years with his mind. Watching MadRogue force Ryuga out of Rider form, Takumi experiences a flow of Sento's memories coming into his mind. Takumi then appears in front of Sento, and asks him if he believed in the power of trust and friendship, regardless of whoever's sins had been done. Sento responds with a smile, and Takumi asks Sento to show him the future he can build, better than he ever did in the past. Takumi and Sento then join hands, and the two assimilate with each other into Sento.

Even after his assimilation with Sento, Takumi continues to exist in form of memories inside his new persona's psyche, talking and discussing with him the matters that Sento can't remember himself: the Lost Bottles and the false death of Shinobu Katsuragi.

As Sento continued to research on Shinobu and with the appearance of another Build, Takumi starts to doubt his father's actions as Sento and he spoke inside their memory world.

After Evolto's defeat, as Sento observes the new world he created, Takumi finally bids farewell to Sento, disappearing from his new persona's psyche.

Kamen Rider Zi-O


As a result of the creation of Another Build by Time Jacker Heure, Kamen Rider Build's history was erased. In the new timeline, Takumi never worked on the Build Rider System and never encountered Evolto, and so never became Sento Kiryu.

After the temporary defeat of Another Build in 2018, Takumi and Ryuga regain their memories and entrust Sougo Tokiwa with Build and Cross-Z Ridewatches. After Another Build's permanent defeat, he permanently loses his memories.

Later, due to another time disturbation by Super Time Jacker Tid, Takumi regains his memories and he, along with Ryuga, Kazumi, and Gentoku aids Sougo against Another Kuuga.

Kamen Rider Grease
Due to the merging of the two worlds, this version of Takumi Katsuragi, along with his father, exists in the new world.

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. This was due to his reasons behind the Build System and his views towards its use after his identity was changed.

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. However, it was revealed the reason why he created the Rider System in the first place was to defeat Evolto, and was appalled to hear Gentoku used it to instigate the Japanese Civil War.

Misora also pointed that Katsuragi, after his memories are restored, behaves just like Sento. But, the difference is that he is arrogant and dismissive to a fault, as he lacks the understanding of friendship of others, comparing that from a. Katsuragi also uses honorifcs in his sentences unlike Sento, who speaks using slang. While desperate in his objective to defeat Evolto, he doesn't seem to express any concern about killing Banjo because of his connection with the alien lifeform.

Forms
Takumi's Build Driver did not originally announce Best Matches, but was modified to do so by Sento Kiryu after Takumi's supposed death.

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 and Kamen Rider Zi-O, he was portrayed and voiced by Atsuhiro Inukai (犬飼 貴丈) who plays his current identity Sento Kiryu as so to hide his alternate identity away from viewers. 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.