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Takumi Katsuragi, nicknamed by his colleagues as "The Devil's Scientist" for his ruthless pursuit of knowledge, is one of the three co-founders of the Faust organization and a minor antagonist in Kamen Rider Build.

Katsuragi was the first to realize how Nebula Gas from the Skywall could be utilized and formed Faust to continue his research covertly. He is the one responsible for inventing devices such as the Build Driver and the Transteam Gun.

He is later revealed to be the original identity of the protagonist, Sento Kiryu and the first Kamen Rider Build before his memories were wiped and his face was altered.

He is portrayed by Yukiaki Kiyama. As Sento Kiryu, he is portrayed by Atsuhiro Inukai.



Takumi Katsuragi was originally one of the top researchers at the Touto Institute of Advanced Matter Physics and the one in charge of studying the Pandora Box. He would earn the nickname "the Devil's Scientist" from his colleagues for his willingness to sell his soul for the sake of research. He later co-founded Faust alongside Night Rogue and Blood Stalk as a way to secretly carry out human experimentation.

During his time at Faust, Katsuragi reverse-engineered the Evol-Driver to create the Build Driver, which he used to transform into Kamen Rider Build.

However, Katsuragi later discovered both Night Rogue and Blood Stalk's true identities, as well as Stalk/Evolt's plans for the Pandora Box and connection to Ryuga Banjou. Katsuragi plotted to stop Evolt, but failed when the alien sneakily switched his fully functioned Build Driver with a dummy one and knocked out immediately. Stalk then swapped Katsuragi's identity with a man named Taro Satou, wiped his memories and killed Satou so he could frame Ryuga Banjou for it.

Stalk later reverted to his civilian identity of his host, Soichi Isurugi and "found" Katsuragi, giving him the new name of "Sento Kiryu".


I am Katsuragi... Takumi Katsuragi...?
~ The Devil's Scientist returns.

After Sento was possessed by Evolt, he had his identity as "Sento" erased when Evolt left his body, causing him to revert back to his identity as Takumi Katsuragi.

Back at nascita, Takumi was confused as to why Ryuga Banjou was helping them, as he had Evolt's DNA within him. He also recognized Misora Isurugi as the one who purified Fullbottles for Faust and told her "nothing personal" about his actions with them. Gentoku Himuro then entered the room, causing Takumi to express a slight surprise.

The two then went outside to talk near the ruins of a fight between Touto and Seito's forces. Takumi commented that he had never expected war to actually break out and had only wanted to defeat Evolt. As Gentoku apologized for his actions as the leader of Faust, Takumi expressed anger at him for deceiving him, stating the Build Driver's only purpose was to defeat Evolt and not to be used for war.

Later on, Takumi accompanied the other Kamen Riders as Build to go fight Evol. He engaged Evol in his Build RabbitRabbit form though, as he had lost his memories as Sento, he did not have the experience to wield it properly. He later bore witness in horror as Nariaki Utsumi defected to Evol's side and became Kamen Rider Mad Rogue.

Retreating to the nascita cafe, Takumi discussed with the other members of Team Build what to do about Evolt, noting that it was odd that he, having destroyed countless other planets, would now want to rule over one. After Ryuga left the room to go sit outside, Takumi announced his intentions to create the Genius Fullbottle and use it to kill both Evolt and Ryuga, stating that, since Ryuga had Evolt's DNA within him it could surface at any time and thus Ryuga could not be trusted. He was later confronted about this while he was working on the Genius Fullbottle by Misora Isurugi, who suggested trusting Ryuga not to turn into Evolt, but Takumi rebuffs the notion as being from a "children's manga".

Takumi later went to fight Mad Rogue as he was leading an attack on Touto, showing up just after Mad Rogue had knocked Kazumi out of his transformation. Cross-Z asks his intentions, but Takumi just tells him he's not there to help him out before transforming into Kamen Rider Build RabbitRabbit form, stating that he figured out how to transform into it by adjusting its Fullbottles more to his liking. He then fights Mad Rogue, who comments that out of everyone, he would have figured that Takumi would understand the most why he had sided with Evolt. Build then tries to transform using the Genius Fullbottle, but finds he cannot use it and instead winds up being forced out of his transformation by Mad Rogue. Cross-Z then steps in and holds Mad Rogue off from finishing off Takumi, telling the scientist he lacks the compassion for others that Sento had and that that's why he can't transform. Watching Ryuga be forced out of his transformation by Mad Rogue, Takumi thinks back to the determination Gentoku showed earlier when he was injured. Spurred on by recent memories of Ryuga and Gentoku, Sento's memories resurface and merge with Takumi's, allowing Sento's personality to come back.

Making a playful remark to Ryuga, Sento announces that "the egotistic superhero has returned" before using the Genius Fullbottle to transform into Kamen Rider Build Genius Form and face off against Mad Rogue.


In contrast to his personality as Sento Kiryu, Takumi is much more cold-minded and ruthless, willing to pursue knowledge at cost, which is what earned him his nickname of the "Devil's Scientist". Though his ultimate goal was to defeat Evolt, Takumi held little concern for the well-being of others. He showed no remorse for the harm his experiments did to Misora while she was with Faust and was even willing to kill Ryuga Banjo if it meant defeating Evolt.

It is strongly suggested that Takumi's current personality was a result of witnessing the Skywall Incident and losing his father, as after losing his memories and becoming Sento Takumi was more caring to others and made sure his experiments with Fullbottle purification did no harm to Misora like they had while he was in his previous persona. Takumi's old personality would later resurface when Evolt restored it and suppressed his memories of being Sento, but "Sento" would eventually return after Takumi realized he could not defeat Evolt without the determination to protect his friends. After Sento resurfaced, Takumi split off into a separate personality and would often converse with Sento inside their head.



Kamen Rider Build


  • Height: 196.0cm
  • Weight: 99.0kg
  • Punching power: 9.9t (right arm) /17.0t (left arm)
  • Kicking power: 23.7t (right leg) /17.8t (left leg)
  • Jumping power: 55.0m (person) Jump)
  • Running power: 2.9 seconds (100m)
  • Special move: Vortec finish!


  • BLD Rabbit Tank Head - Kamen Rider Build Rabbit Tank Foam Head.
    • Light Eye Tank - Kamen Rider Build visual sensor. It is possible to increase the hit rate by instantly calculating the trajectory when making a shooting attack.
    • Cannon Face Module - A shooting enhancement device installed on the head of Kamen Rider Build. It is possible to increase the power of the equipped shooting weapon and increase the range and explosive power at the time of impact.
    • Panzer Head Armor - Blue armor parts that protect the head of Kamen Rider Build. By stacking several types of armor plates with different properties, the strength against physical attacks is increased.
    • BLD Signal - Kamen Rider Build data collection device. It is possible to aggregate battle data in real time and accurately grasp the abilities of yourself and the enemy. It also manages the condition of the whole body, and if there is a damaged part, it automatically performs emergency repair.
    • Wildhead Armor - Red armor parts that protect the head of Kamen Rider Build. It is strong enough to withstand normal smash attacks, and is also lightweight to improve athletic performance.
    • Ear Face Module - A hearing enhancement device installed on the head of Kamen Rider Build. By catching the signs of the enemy and slight movements, the next action is predicted and a quick counterattack is possible.
    • Left Eye Rabbit - Kamen Rider Build visual sensor. It has increased reaction speed and accuracy in combat, and also incorporates a special olfactory sensor to find hidden enemies.
  • Wild Chest Armor - Lightweight armor that protects the chest of Kamen Rider Build. It is strong enough to withstand normal smash attacks, and is also lightweight to improve athletic performance. It is also possible to speed up any movement of itself for only a few seconds.
  • BLD Rapid Shoulder - Armor that protects the right shoulder of Kamen Rider Build. Optimizes arm movements and improves attack speed.
  • BLD Unlimited Suit - Kamen Rider Build shock resistant bodysuit. At the same time as protecting the transformant from combat damage, it is possible to release the physical limiter and bring out the hidden physical ability.
  • Quick Rush Arm - The right arm of Kamen Rider Build. The power of the punch to be delivered is a little low, but he is good at attacking with a lot of effort by taking advantage of his high agility.
  • BLD Rapid Gloves - Reinforced gloves that cover the right fist of Kamen Rider Build. Because it can move finely and quickly, it is good at attacking with weapons such as drill crushers.
  • Heavy Assault Rifle - The right leg of Kamen Rider Build. It has excellent mobility and defense, and is good at heavy kicks that hit high-strength armor plates.
  • Tank Roller Shoes - Battle shoes that protect the right foot of Kamen Rider Build. It has a built-in track device that enables high-speed driving, and you can also use it to scrape off the enemy's armor.
  • Panzer Chess Armor - Composite armor that protects the chest of Kamen Rider Build. By stacking several types of armor plates with different properties, the strength against physical attacks is increased.
  • BLD Impact Shoulder - Reactive armor that protects the left shoulder of Kamen Rider Build. It is possible to expose an object in contact with a shock wave and destroy internal functions. Its power is comparable to the shock wave when a tank gun is fired.
  • Build Driver - A belt used when transforming into Kamen Rider Build.
  • Heavy Assault Rifle - The left arm of Kamen Rider Build. The drive device built into the inside enhances the strength, and it is possible to deliver a heavy punch that echoes to the internal center of the enemy.
  • BLD Impact Gloves - Reinforced gloves that cover the left fist of Kamen Rider Build. Reactive armor is attached to the back of the hand, and it is possible to destroy the internal functions of the enemy with a punch accompanied by a shock wave. Its power is comparable to the shock wave when a tank gun is fired.
  • Quick Rush Leg - The left leg of Kamen Rider Build. It has high agility and can perform high jumps using the jump strengthening spring "Hop Springer".
  • Rabbit Foot Shoes - Battle shoes that protect the left foot of Kamen Rider Build. We are good at light footwork, and it is possible to launch a kick attack that interweaves acrobatic actions such as Moonsault.


Takumi Katsuragi

Kamen Rider Build


  • It was also revealed in Kamen Rider Heisei Generations FINAL: Build & Ex-Aid with Legend Riders, that Build who appeared in the 44th episode of Kamen Rider Ex-Aid and Kamen Rider Ex-Aid: True Ending is Takumi, before his loss of identity. This was teased in a TV spot following the premiere of the film. His usage of "see you" (in English instead of Japanese) when he bid farewell to Kuroto Dan is also a hint.
  • Him being the founder of Faust and at the same time being called "the Devil's Scientist" alludes to the titular character of the namesake German tale in which the organization he founded is named after; a scholar who made a pact to the Devil exchanging his soul for unlimited knowledge and worldly pleasures.
  • He is similar to Kuroto Dan from Kamen Rider Ex-Aid as both were the founders/creators of the villain factions of the series as well as the creators of the protagonists' Kamen Rider powers. Just like Kuroto, Katsuragi debuted in his series' predecessor, but he was in his respective Kamen Rider identity, and he wasn't played by his actor. Katsuragi also cared for both his parents despite being a villain, similar to Kuroto's love for his mother. However, unlike Kuroto, Katsuragi redeemed himself.

External links


           BUILD LOGO.png Villains

Night Rogue | Blood Stalk | Takumi Katsuragi | Nariaki Utsumi | Shingo Kuwata | Eita Kawai | Masahiro Nabeshima | Norio Matsui | Yoshikazu Takahashi | Shinobu Katsuragi | Faust Guardians

Yoshiko Tajimi | Blood Stalk | Kazumi Sawatari | Hokuto Three Crows | Akaba | Aoba | Kiba | Massugu Ubukata | Hokuto Guardians

Masakuni Mido | Kamen Rider Rogue | Fu Washio | Rai Washio | Seito Guardians | Hard Guardians

Namba Heavy Industries Ltd.
Juzaburo Namba | Nariaki Utsumi | Fu Washio | Rai Washio | Sawa Takigawa | Kaisei Mogami | Guardians | Hard Guardians

Blood Tribe
Killbus | Evolt | Kengo Ino | Ryoka Saiga | Mitsuomi Gohara

Needle Smash | Strong Smash | Burn Smash | Flying Smash | Press Smash | Ice Smash | Stretch Smash | Fang Smash

Simon Marcus | Keiji Uraga | Phantom Crushers | Guardians | Hard Guardians