Characters / Kamen Rider Build (Sento Kiryu)

Main Character Index | Protagonists (Sento Kiryu/Kamen Rider Build) | Faust (Blood Stalk) | Touto Government | Hokuto Government | Seito Government | Namba Heavy Industries | Movie-Exclusive Characters

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This is a partial character sheet for Kamen Rider Build. Visit here for the main character index. Subjective trope and audience reactions should go on the YMMV page.

This page details tropes for Sento Kiryu for Kamen Rider Build.

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Sento Kiryu/Kamen Rider Build

Portrayed by: Atsuhiro Inukai (live), Seiji Takaiwa (suit)

The Genius Physicist

"I've found the winning formula!"

The main protagonist, Sento is a self-proclaimed handsome and brilliant theoretical physicist suffering from amnesia that made him forget the last 20 years of his life. He transforms into Kamen Rider Build in order to fight the Smash and learn the truth about himself. His genius mind enables him to create Build and Cross-Z's equipment.

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Tropes that apply to him in general

• Amnesiac Dissonance: Acknowledging it is part of Sento overcoming his Heroic BSoD in #16. Neither the person whose face he's taken nor the person he was before would have become a hero, even if given the chance: only Sento Kiryu did.
  • Late in the series, it's implied that Sento is very similar to what Takumi Katsuragi was like before the Sky Wall Incident, based on how he acts both in flashbacks to that period and how he remains unchanged even after having his memories up to the Sky Wall incident restored. Takumi, however, has been shaped by the ten years after the Sky Walls into a much different person.
• Amnesiac Hero: He has no memories prior to his escape from the lab where he was experimented upon. This is because Soichi removed it. It was revealed that Nebula Gas experimentation only alters memories for several hours.
• Anti-Hero: Implied: His premiere appearance in Kamen Rider Ex-Aid, had him show up to take a sample of Emu's essence and then, in contrast to how new and old Main Characters would briefly team-up during the finale of the current series, leaving the heroes to deal with the pandemic themselves. This event occurred before his memory loss, back when he was the much less scrupulous Takumi Katsuragi, who is far more anti-heroic than his current personality as Sento.
• Animal Motifs: While most of Sento’s forms as Build involve a different animal, examples being Hawk/Gatling or Rocket/Panda, the biggest and most prominent one is rabbits. His base form is Rabbit/Tank, his hair tends to flip up like a Rabbit’s ear when he’s excited or scratches his head, his first major powerup and penultimate form and even final forms involve Rabbits. Even when possessed by Evolt briefly, he used a Rabbit Evolbottle.
• Badass Bookworm: Sento is proficient with firearms, can ride his bike at high speeds, and has decent hand-to-hand fighting skills even when he isn't Build.
• Bash Brothers: Sento and Ryuga show shades of this in his pre-Rider days, with them falling into this kind of relationship once he becomes Cross-Z. Most of their conversations between battles consist of throwing shade at each other, approaching a full-fledged Boke and Tsukkomi Routine, but they come together the moment a threat arises. Once Kazumi changes to their side, there is a brief period where it seemed he and Sento would form a pair over Ryuga and Sento, but with the arrival of Cross-Z Magma and Rogue's turn to good, Sento and Ryuga quickly re-established themselves as the alpha pairing. They have the best sync in fights and their much higher power levels means they are the combat team to Grease and Rogue's support.
• Berserk Button: Calling cruel weapons like the Transteam Gun's Devil Steam as "inventions" is a quick way to draw Sento's ire. Taunting him with the secrets of his past is a much faster way, at least before he knew.
  • Don't hurt his family. He will think up some creative way to strike back and no one is going to like it.
• Big Ego, Hidden Depths: Its surprisingly easy to look beneath underneath Sento's narcissism and discover a man completely at a lost of just what his place in the world is but none the less tries to be the best human being he can possibly be.
• Catchphrase: His pre-battle catchphrase is "Now, shall we begin the experiment?" This came up when he first tried transforming to Build, as he didn't know what he was doing, at all, so it was a thing that just stuck.
  • When things are going his way, he says "This is the best!"; by contrast, when they don't he says "This is the worst!". He tends to say one or the other at least Once an Episode.
  • He also tends to say "hang on" or "wait a second" before following up with an attack.
  • When he turns into Build he uses "The law of victory has been decided!"^note As indicated by the title of a late-series insert song, "Law of the Victory"; alternate translations include "I've found the formula of victory!", "I've found the winning formula!", and "Victory conditions have been cleared!"^note The latter from the Puzzle & Dragons crossover event
  • He uses "Build up!" when changing forms.
  • He had "the handsome and brilliant physicist Sento Kiryu!" to refer to himself every time during recap. He drops it after the war situation become more severe.
  • A minor example, his victorious genius routine: "Ain't I great? Ain't I awesome? Ain't I a genius?" every time he admired his own work and "How do you like, my in-ven-tion?" when he bragged about his invention to others.
• Character Tics: As noted by his father, Sento makes the habit of messing with his hair whenever he is anxious, upset, or excited.
• Chronic Hero Syndrome: Sento just can’t let anyone suffer if he can stop it. No matter what, he will attempt to save whoever he comes across.
• Contrasting Sequel Protagonist: Sento is obviously more acerbic than his predecessor Emu Hojo, and where Emu was a poorly-respected member of a well-respected profession, with the backing of the Japanese government, Sento is well-respected by his peers but a criminal in the government's eyes. Despite the points of contrast, though, both are equally driven by the basic desire to help people, and prioritize the health of others over their own needs. In an unusual case, Sento can also apply the contrast to Ex-Aid's Deuteragonist Kuroto Dan, as both have an Insufferable Genius nature and created their own belts and weaponry, with the difference being that Sento is genuinely heroic where Kuroto is a Heroic Comedic Sociopath at the best of times.
• Cutting the Knot: Sento seems to favor the no-nonsense solution whenever the option is available. An early example involves him taking a hammer to his own basement wall as soon as the evidence suggests that this is a good idea.
• Darkest Hour: Sento's occurs not during the series, but in Be The One. He's been completely isolated by the Blood Race, who brainwashed all of Japan (including Banjo, Misora, and Sawa) into hating Build, and captured Kazumi and Gentoku since they can't be brainwashed. After being defeated by Banjo, the Big Bad Kengo Ino rips open the old wound of Build being a "fake hero", and even his faith in science seems to have failed him. After angsting for a while and debating the Takumi personality, Sento declares that even if the world hates him and everything he believed in was fake, there are still some undeniable truths: his bond with Banjo, and his father's belief in Love and Peace, which gives him the resolve to keep fighting and save the world.
• Deadpan Snarker: Has got snark and sarcasm for days.
• Determinator: Just like Ryuga. Sento is made of iron, justice and occasional suicidal tendecies, so when he sets his mind on something, not even the end of the world is enough to stop him.
• Did You Just Flip Off Cthulhu?: He constantly delays Evolt's plans. As of #41, Evolt is so angry he promises that he won't kill Sento before crushing everything he has down to the last hope.
• Dissonant Serenity: He can keep calm, detached attitude on deeply unsettling occasions like the revelation of his identity or war breaking out pretty much in his backyard. It's apparently his defense mechanism to keep himself focused on the task at hand without getting distracted by his emotions. It usually works only until he is called out on it or more things are heaped on him.
• Driven to Suicide: Sento attempts to commit suicide by self-destruct switch in #22, traumatized by the monster the Hazard Trigger turns him into. Misora calls him out on both the suicide attempt and forcing her to be the one to push the button, and thanks to Sawa and Ryuga, he doesn't go through with it.
• Dull Surprise: His reaction to things that don't concern him, someone (like Ryuga) doing something stupid and most of the overall silliness inherent to his team.
• Empty Shell: Sento's first use of the Hazard Trigger leaves him so horrified by what he proceeds to do under its influence that he's left a depressed wreck. To accentuate this point, in #21, most times when his face is shown, his eyes are framed in such a way that they look completely black.
• Even the Loving Hero Has Hated Ones: His ego is only eclipsed by his drive to help others and preserve life. However, Evolt and Killbus are the only exception to this rule thanks to their Omnicidal Maniac tendencies.
• Family of Choice: He eventually comes to think of the entire nascita gang as his true family.
• Fashionable Asymmetry: Not as apparent as his Rider form, but he wears two different colored sneakers - one red, the other blue.
• For Great Justice: His motivatining mantra is that he fights for “love and peace”.
• For Science!: Sento believes that science is neither "good" nor "evil"; like any other tool, it all comes down to how it's used. That said, he considers some inventions like the Sclash Driver and Hazard Trigger too dangerous to ever use.
• Genius Bruiser: Sento is a physicist and the most intelligent of the Heisei Riders, while being as combat-capable as all the other Riders are. Thanks to his elevated Hazard Level, his physical abilities are mildly superhuman even when not transformed.
• Good Feels Good: He enjoys the feeling of helping people, and notes that it always puts a smile on his face to save someone from, or from being a Smash.
  "It puts a smile to my face, you know. Helping people. Not that you can see with the mask on."
• Guile Hero: When the situation calls for it, he has shown to have the capability of properly pulling off a Batman Gambit, even managing to Out Gambit Evolt on more than one occasion. Most prominently at the end of the series.
• Heroic BSoD: When Sento encounters a source of emotional distress too great to deflect, he tends to shut down entirely. #16 and #21 feature prominent examples.
• Heroic Willpower: Manages to resist Tid's mind control in Heisei Generations Forever.
• He's Back!: Pulls this off twice through-out the entire series, once in #16 after a pep-talk from Banjo. Of note especially is when he regains his memories of being Sento Kiryu after having reverted to being Takumi Katsuragi, which he follows up on by transforming into Build Genius Form for the first time.
• Idiot Hair: Often happens when he does something silly, gets ahead of himself or gets an idea, though it appears from the side of his head instead of up top. Taro Satou had all of his hair like this.
• Insufferable Genius: He loves bragging about his inventions whenever he gets the chance, but is still a lot more amiable most of the time than expected from this trope.
  Opening narration: "The handsome and brilliant physicist Sento Kiryu!"
  After finishing something: "Ain't I great? Ain't I awesome? Ain't I a genius?"
• Irony: For all of his claims of love and peace at the end of the day Sento is the one person that is unwilling to move on from his life as a Kamen Rider. His new lab is a near exact replica of the Nascita basement. He still stupidly keeps the white panel around instead of destroying it, The Killbus spider is essentially Ryuga's morpher but better sold as a children's toy, and when Gentoku and Kazumi came knocking he was quick to restore their powers.
• Jerk with a Heart of Gold: Sento can come across as a narcisstic sociopath to strangers, but he will fight to save all lives he can and forever blame himself for failing that even if he didn't have a chance in the first place, like saving Ryuga, an escaped convict, from being used a fodder for experimentation. One of his catchphrases is narcissisic, conceited hero of justice for a reason.
• Laser-Guided Amnesia: He can't remember much about 20 years of his past, save for that he was experimented on by Night Rogue.
• Like Brother and Sister: He forms this sort of bond with both Banjo and Misora. Banjo eventually becomes a brother to be trusted with his life while Misora is the little sister to be teased and protected.
• Manchild: A downplayed example. Sento is usually the responsible one to Ryuga, but there are moments when he acts like a child (petulant or other). Also, there are hints of Psychopathic Manchild turning up at the rare occasion he jokingly threatens someone with his newest weapon after building it.
• Meaningful Name: Sento's name is composed of the first kanji for tank (戦車 Sensha) and the kanji for rabbit (兎 To). Knowing the person who gave it, Soichi most likely gave it with the meaning intended. Confirmed in the recap segment at the start of #9, where Ryuga raises the point, Soichi explains the name and Sento incredulously shouts, "So you just named me RabbitTank?!"
  • Averted with his surname, Soichi just took it from his favorite barber shop. There is still some significance to it as it's second kanji is for life (生 ikiru), matching Sento's Thou Shalt Not Kill attitude and Katsuragi's new life as Sento.
    • Looking at it in a different angle, " Kiryu " can be broken down to " Ki " and " Ryu ", the former being homophone to " Key " while the latter means " Dragon " in Japanese, one of Build's form consist of these as a Best Match.
  • It also applies to Taro's name, only not quite as literal: his first name is based on the EH500 Kintaro Tank freight train, and his last name is the same with the protagonist of a Japanese children picture book, Sato-kun the Rabbit.
• Neat Freak: By his own admission, he is this. Which completely shocks him when he sees 'his' former identity's room.
• Nice Job Breaking It, Hero: On at least two occasions.
  • The first is him completing Kasturagi's development of the Sclash Driver, which by the way exposes the user to the full effects of the Nebula Gas, making them more violent with prolonged usage unless they somehow overpower its effects. This leads to the birth of Kamen Rider Grease and Rogue, the latter of which was by far one of Sento's more dangerous foes until Evolt got his hands on his own belt. To be fair to Sento, Blood Stalk and Gentoku tricked Sento into completing it since he had no idea about the belt's nasty side-effects.
  • The second time Sento screwed up, again for reasons he couldn't have known otherwise, is arguably much worse. His decision to keep the White Panel of the Pandora's Box instead of destroying it gave Killbus free entry into the new world.
• Not Worth Killing: After they steal all the Fullbottles he had on his person at the end of #10, Night Rogue and Blood Stalk opt to leave him wounded in the dirt instead of finishing him off. They still need him to purify the remaining Fullbottles and finish the Sclash Driver, after all.
• Perpetual Frowner: The events from #17 onward put Sento through a long period of being unable to smile. It's not until ten episodes later that things finally begin to look up for him.
  Ryuga: He doesn't smile anymore, you know?
• Phlebotinum Rebel: Was one of the individuals who were captured and experimented by Faust, or rather, his current personality was created by Evolt to do his dirty work behind his back before he starts to opposed him for good. He was also the captor and experimenter himself before this happened.
• Quest for Identity: Knee deep in it, still nowhere near getting to know who he really is and each turn provokes more questions then it gives answers. A Red Herring is floated before #15 finally reveals his true identity: Takumi Katsuragi, the Devil's Scientist himself. It isn’t until the mid point of the series that he declares that his current personality is enough of an identity on its own.
• Red Oni, Blue Oni: The blue to Banjo's red. Not only is Sento the intellectual of the two, the Tank Halfbody's color is blue.
• Science Hero: He's a physicist who happens to be a Kamen Rider. He even makes his own gear!
• Say My Name : EVOLT!!! Evolt sauntering on the scene as if nothing happened despite being in the middle of The End of the World as We Know It that he caused was just too much.
• Silly Rabbit, Cynicism Is for Losers!: When others denounce his “love and peace” mantra as overly simplicity and childish, he responds with this. He knows that it’s unrealistic and will lead to heartache for himself, but still says that it’s more than enough of a goal for him to never stop fighting for.
• Stepford Smiler: Like his pre-amnesiac self, Sento's default response to emotions he doesn't feel comfortable expressing is to deny they exist. It works if the problem he's dealing with isn't too big, but the strategy fails him more and more as his situation worsens.
• Talking to Themself: He occasionally converses with his original self in a mindscape with doors, equations and gears after regaining his memories and becoming the identity in control. It goes as well as a conversation between a staunch cynic and optimist can.
• Think Nothing of It: As he explains to Ryuga, he doesn't consider helping people to be justice if you expect a reward for doing it.
• Thou Shalt Not Kill: He has a strict policy against killing his opponents or letting innocent bystanders die. Which is partially why the revelation that he was Katsuragi, a scientist who performed lethal experiments on human test subjects dozens of times hurts him rather badly, and what he does under the influence of the Hazard Trigger breaks him outright.
• Trauma-Induced Amnesia: It is safe to say that the cause of his amnesia is all the experimentation done on him by Faust's scientists.
  • Or so he is led to believe. Then in #15, it was revealed that this is because Soichi removed his memories. The experimentation only altered his memories of several hours.
• Unwitting Pawn: Most of Sento's actions prior to #14 are playing into Faust's hands. Even afterward, he quite willingly finishes designing the Sclash Driver, allowing Blood Stalk to steal its data and give one to Hokuto. It isn’t until late in the series that he finally slips all outside control and completely turns the tables on his manipulators.
  • Surprisingly enough though, he manages to invert his status as this by turning Evolt, the main orchestrator of the events that occur in the series, into HIS pawn by taking Evolt's gathered energies and using them to create a new world without the Sky Walls.
• World's Smartest Man: Has been repeatedly stated to have the highest IQ of any Heisei Kamen Rider.

Tropes that apply to his past self (unmarked spoilers)

Takumi Katsuragi

Portrayed by: Yukiaki Kiyama

The Devil's Scientist

The researcher originally in charge of studying the Pandora's Box, a brilliant man known as "The Devil's Scientist" by his colleagues. Ryuga was arrested for his murder prior to the series, and discovering the mystery behind Katsuragi's murder is his main motivation.

He was a founding member of Faust, the original planner of Project Build, and most importantly, the true identity of Sento Kiryu.

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• Anti-Hero: Once his full motivations are revealed, it's clear that Katsuragi was seeking a good end, but for vengeance rather than justice. Unlike his current personality as Sento, Katsuragi is willing to get his hands dirty in order to defeat the likes of Kaisei Mogami and Evolt, even as far as to steal Ex-Aid's powers or try to kill the yet-to-be awakened Ryuga just to achieve his goals, but that same willingness to do anything to kill Evolt was what let the snake take advantage of Katsuragi's brilliance to help get his plans rolling.
• Back from the Dead: Either as a side-effect of his possession or as a deliberate act of spite, Evolt's theft of Sento's body causes Takumi's memories and personality to return and Sento's to vanish. It only lasts for a few episodes before Takumi willingly "dies" a second time.
• Catchphrase: Episode 39 shows that Sento's catchphrase "Isn't it great? Isn't it amazing? Aren't I a genius?" started with Katsuragi, but he delivers it in a much more arrogant manner.
  • When he is Build his catchphrase is "Kamen Rider Build, build as in to create." best shown during Build's early cameos in Ex Aid when Katsuragi was the one using it.
• Cold Ham: He loves science just as much Sento, but since he is stoic and reserved compared to his much more excitable other self, he naturally expresses it in a way as cold as to give someone a frostbite.
  • In ROGUE special, he bolts towards the research equipment at Faust's base in the same way Sento typically reacts to stuff that interests him, but his expression doesn't change nor does he say anything.
  • He has the same victorious routine after inventing something as Sento has, but performs it without any childishness or excitement.
• Comfort Food: Tamagoyaki ^note basically an omelette served in rolls prepared by his mother. He apparently liked it so sweet that it's unbearable for anyone else to eat.
• Creative Sterility: Of a sort. He's certainly not starved for ideas, but he's so stuck in his ways and distrusting of others that he can't properly use Build Genius and ultimately can't utilize the Build System itself because his emotional mindset is too dulled to bring out its full power. His conversation with Sento in a representation of his mind shows formulas and gears stuck statically in place that only start moving again once he puts Sento back in the driver's seat. The real fault in his creativity, however, is one he shares with Sento: they both respond to problems by building weapons instead of thinking about how to use the Rider System and its components constructively, which blinded them both to the real functionality of the Hazard Trigger.
• Dissonant Serenity: His eager and professional demeanor never falters during his device showcase videos, even when he's talking about how some of them have lethal, mind-destroying side effects. This partially carries into Sento's habit of using this state as a defense mechanism in traumatic situations.
• Everyone Has Standards:
  • Even for Katsuragi, the Hazard Trigger was too much, as was the discovery of Stalk and Ryuga's shared true identity. The real reason he brought both to his house was to try and kill them.
  • Near the end of the first part of the ROGUE miniseries, he's noticeably uncomfortable when Gentoku repurposes his underground research facility into the starting point of Faust.
  • Heisei Generations FINAL reveals that he helped build Kaisei Mogami's Enigma device, and even used it to travel to the main Kamen Rider universe and steal Emu Hojo's powers, but the moment he found out about Mogami's plan to forcibly merge the two worlds (which would destroy them both) he tried to pull the plug.
• Foil: It's clear that he and Sento are two completely different people/personalities when you break it down.
  • Relationships: Sento, despite his smug behavior, has complete trust in his allies, cares for Misora as a clear friend, and despite bickering with Ryuga several times, they are clearly best friends. On the other side, Takumi trusts nobody, sees Misora as nothing but a means to create FullBottles, and was actively trying to kill Ryuga due to the latter containing Evolt's DNA.
  • Use of the Build Station. Even though Takumi built the Build Driver and powers, he was unable to handle the more powerful forms Sento created, and had to adjust the RabbitRabbit form for his own goals. Sento had at least a year to train with the Build system, went through multiple different Best Matches with different abilities, and was easily able to adapt to any situation.
  • And finally, their beliefs. Sento wanted to use the Build system as a way to protect people, and believed that science should be used to help instead of destroying. Takumi wanted to use the Build system to defeat Evolt, which turns into a plot point when he could not use the Genius FullBottle as his desire was not compatible with Sento's sense of justice.
• Genius Sweet Tooth: As noted above, Takumi's preferred preparation of Tamagoyaki is considered to be very sweet compared to how it is usually served and him fulfilling the genius aspect serves little explanation given his scientific background and his hand in creating the system used by the Riders.
• Good Is Not Nice: When his memories return late in the series, his primary goal is to defeat Evolt to save humanity. However, he dismisses anyone of "lesser" intelligence, treating Sento's friends and allies as little more than gibbering chimps and refusing to hear any debate about sparing Banjou's life because they can't offer it in a logical manner.
• Heel–Face Door-Slam: Played with. He attempted to quit Faust and kill both Blood Stalk and Banjo upon discovering that they were the mind and body of Evolt, only for Stalk to have outplayed him by swapping Katsuragi's Build Driver for the nonfunctional prototype. Stalk then wiped Katsuragi's memory and changed his appearance, turning him into Sento. He still ended up becoming a good guy, but in a way that, initially, served Stalk's plans rather than ruining them.
• He's Back!: In the absolute worst way. Raising his Hazard Level into the 6.0 range and subsequently being possessed by Evolt restored his memories at the cost of Sento's personality disappearing.
• How Do I Shot Web?: To his frustration, he's barely able to use Sento's upgrades due to his lack of experience despite having been the major architect of the entire Rider System.
• Like Father, Like Son: Turns out his father was also involved in human experimentation, with Ryuga as a test subject.
• Last Chance to Quit: The usually rabid and reckless Gentoku gave him ample opportunities to scrap Faust before they went past the point of no return, but Katsuragi pressed on anyway, believing their experiments, as monstrous as they would inevitably become, would benefit human civilization in the long run.
• Mad Scientist: He was the first to conceive of Nebula Gas technology, and at least for some period he was entirely comfortable with human experimentation. It still shows up in his new personality, Sento Kiryu, but to a lesser degree.
• My God, What Have I Done?: After his return, he dissolves his relationship with Gentoku once he learns that in spite of all they had sacrificed to create the Rider System, the nightmare scenarios they tried to prevent with its usage (Evolt's return to power and a Japanese civil war respectively) still came to pass.
• Not What It Looks Like: Heisei Generations FINAL reveals that he was the Build who appeared in Ex-Aid: True Ending and stole Emu's powers, seemingly being his usual "Devil's Scientist" self. Later in the movie, Sento finds Katsuragi's notes and discovers that he was trying to save Ex-Aid's powers, believing that Hyper Muteki was the only thing capable of stopping Mogami's plans but realizing that his powers would be affected by the two worlds merging.
• Posthumous Character: Initially alleged to be dead before the show even begins, before it's revealed that he was The Hero all along.
• Power Incontinence: During his return and loss of his memories as Sento, Katsuragi realizes that he can't keep up with the current Build upgrades.
• Red Baron: "Devil's Scientist".
• The Reveal: While the audience had plenty of reason to guess it beforehand, #15 finally confirms that Katsuragi lives on as Sento.
• Split-Personality Merge: Averted as the solution to his and Sento's situation: after Sento becomes their dominant personality again, he gets Katsuragi's childhood memories, but not the ones from his adulthood. Instead, Katsuragi's personality containing those memories sticks around as a Spirit Advisor.
• So Last Season: Interestingly, Build is not this it's gained considerable power while he was gone, but his skill at using it is. He'd only ever had base RabbitTank and GorillaMond as his options before becoming Sento who'd created dozens of new forms and features for it in the year he'd been in the drivers seat. Upon returning, Katsuragi is nigh useless at first because he can't control the Hazard Trigger new forms very well at all, and the basic Best Match forms he could use are unavailable because of the bottles being taken. He's able to adjust Rabbit Rabbit down to his level and gets the hang of the Fullbottle Buster enough to be effective again, but he quickly finds himself unable to make the most of the system and puts Sento back in control.
• The Starscream: He worked with Faust while intending to kill Evolt from the very beginning to avenge his father.
• The Stoic: In life, he was phenomenally bad at expressing his emotions. He even kept an even, level face while eating his favorite food. That being said, it was just expressing those emotions he was bad at. He still dearly loved his mother, despite never telling her such, and left her a coded message in his final message thanking her for giving him life.
• Straw Vulcan: During his return in #37-39, he dispassionately dismisses the rest of the cast's silly antics and belief in friendship as nonsense straight out of a shonen manga while planning out a way to destroy Evolt...and Banjo, whom he believes will become another Evolt if left unchecked. However, despite having created the Genius Bottle himself, he's unable to use it because he doesn't have the right emotional mindset; after he regains all his memories and becomes the emotional Sento Kiryu again, the Genius Bottle works perfectly, creating Build Genius Form.
• Then Let Me Be Evil: It's shown in a flashback that Katsuragi accepted that his desire to advance the world through Faust and Project Build would lead to suffering, but such was his fury and resolve that he declared he would even sell his soul to the devil if it was for the sake of research.
• Walking Spoiler: Just like Himuro, it's impossible to discuss his role in this series without spoiling huge plot twists. After all, he is our protagonist.
• Well-Intentioned Extremist: Katsuragi is implied to have had sympathetic motivations for creating Faust, but the monster he created grew far beyond his control. When he learned who Evolt was, he tried to kill him and his other host Banjo before he could set into motion his plan to destroy the world.
• Who's Laughing Now?: Furious that the nation drove his father to suicide by blaming him for the Sky Wall Disaster, he decided to reclaim his family's honor by creating weapons derived from the anomaly's Nebula Gas deposits.
• Would Hurt a Child: He exploited a preteen Misora's abilities dozens of times to create his FullBottes. His incredibly backhanded apology for it when he returns stuns the usually fierce girl with its sheer glib audacity, much to Ryuga's ire.

Tropes exclusive to him as Kamen Rider Build

Are you Ready? Hagane no Moonsault!^note Steel Moonsault! RabbitTank! Yeahhh!

Are you Ready? Shuwatto Hajikeru!^note The Effervescent Burst! RabbitTank Sparkling! Yea-Yeahhh!

Are you Ready? Uncontrol Switch! Black Hazard! Yabei!^note OH NO!

Are you Ready? Overflow! Kurenai no Speedy Jumper!^note The Crimson Speedy Jumper RabbitRabbit! Yabei! Haei! ^note Woah! Fast!

Are you Ready? Kanzen Muketsu no Bottle Yarō!^note The Completely Flawless Bottle Guy! Build Genius! Sugei! Monosugei!^note Awesome! Seriously Awesome!

Are you Ready? Rabbit! Dragon! Be the one! Cross-ZBuild! Yeahhh! Yeahhh!

• 11th-Hour Superpower: In the final episode, Sento uses the Gold Rabbit and Silver Dragon Fullbottles to transform into Build RabbitDragon Form, which is completely different from the Cross-ZBuild Form seen in the movie.
• All Your Powers Combined: Genius Form lets him access the power of all 60 Fullbottles at will. However, this is only seen in #42, where Build is able to use the Diamond Fullbottle's shielding powers to defend against Evol's Steam Attack; in all other episodes, Genius exclusively uses its own Flash Step and healing powers.
• Awesome, but Impractical:
  • KeyDragon is the most powerful of the first ten Best Matches by a considerable margin, easily standing up to Night Rogue and Blood Stalk when other Best Matches can't. However, Dragon is so powerful that even Lock can't properly control it, with explosive results. Since Ryuga's unusually high compatibility with Dragon allows him to use it to achieve a Rider form all on its own, KeyDragon is swiftly retired, with Lock becoming Ryuga's backup Fullbottle of choice. Sento later usesKeyDragon Hazard against Kamen Rider Evol after the latter possesses Ryuga.
  • The Hazard Trigger's berserker state is as cool and powerful as it is terrifying, but its inability to tell friend from foe makes it vulnerable to any opponent tough enough to not get completely crushed by its opening salvo of finishers, as they can easily refocus its attention onto one of Sento's allies.
• Badass Bandolier: The Gatling Fullbottle gives him armor on the left shoulder that evokes this.
• The Berserker: Using the Hazard Trigger allows Sento to upgrade any Best Match into a solid black Hazard form. Using this form for too long will cause the user's mind to be overwhelmed, causing them to rampage and attempt to destroy everything in sight. Even Katsuragi thought it was too dangerous to ever use.
• Big "NO!": The Hazard Trigger prompts the Build Driver to switch from its usual punctuation of the transformation with a loud "YEAH!" to one of these. It's entirely warranted.
• Broke Your Arm Punching Out Cthulhu: Sento's plan in the penultimate episode empties out the Genius Bottle, leaving him unable to use it for the final battle.
• Combat Pragmatist:
  • Part of what makes Hazard forms so terrifying is invoking this, as they trade Sento's usual flashy fighting style for a brutal and straightforward one with all of his immense brainpower suddenly focused on nothing but the most efficient way to kill everyone in sight. A sufficiently clever opponent can turn this trait against Sento by getting him to focus on murdering one of his own allies first.
  • Sento's not above this when he's in full control either - upon gaining a Flash Step in Genius Form, he starts spamming it gratuitously.
• Combat Tentacles: The Octopus Fullbottle gives Build the ability to use the tentacles on the Twist Lash Arm mantle for long range grabbing.
• Cool Sword: The Drill Crusher, a drill-shaped sword that can turn into a gun.
  • He builds another one for use by the NinninComic form called the 4-Koma Ninpoutou, which can switch between four attacks: Art of Cloning, Art of Flame, Art of Wind, and Art of Camouflage.
  • He builds yet another one for use with the RabbitRabbit and TankTank forms called the Fullbottle Buster, which like the Drill Crusher, can be used as a gun. Then again, "cannon" would be more appropriate than "gun"...
  • Sento also used the Beat Closer when using KeyDragon Hazard Form in #35.
• Dangerous Forbidden Technique: The Hazard Trigger grants Sento access to Hazard Forms that exceed even Sparkling and the Sclash Driver riders in power, HawkGatling Hazard even being so fast it appears to teleport. The catch is that Sento's mind is overwhelmed by the Trigger when it's used, turning him into an emotionless berserker that won't let up until everything in sight is dead. Not defeated. Dead.
• Deadly Rotary Fan: The Helicopter FullBottle grants one that can be used either for flight or as a sword.
• Dual Wield: Any of Build's weapons can be used in any form, or even when not transformed at all, so he occasionally uses the Drill Crusher as an off-hand weapon for the 4koma Ninpoutou or HawkGatlinger. Sento's fighting style in RabbitTank Sparkling tends to cycle through many of Build's weapons in rapid succession, so he makes much more frequent use of two weapons at once in that form.
• Elemental Powers: Every type of element there is has at least one Best Match associated with it, with some having more than one. If Build's current form can't use a given element on its own, the Drill Crusher can provide it on demand with a Vortex Break.
• Evil Costume Switch: His Hazard forms are a Superpowered Evil Side, and their design is pitch black, spikier, and generally far more menacing than his base forms.
• Evil Knockoff: The Build Driver is actually a good, though still lesser, knockoff of the Evol Driver.
• Experienced Protagonist: By the time we first see Build in person, he's been at large for about a year.
• Fashionable Asymmetry: Build's suit almost completely has the appearance of strips of color (or of black, for the undersuit) wrapping around him at a 45-degree angle.
• Finishing Move: All of his Best Matches each allow him to use a Vortex Finish depending on the form, though certain weapons have attacks that can rival a Vortex Finish:
  • RabbitTank: Build dives underground to send a white energy chart flying up to the surface with the dotted line securing the enemy before leaping back up, and delivering a Rider Kick whilst riding the chart's line.
  • GorillaMond: After fabricating a wall of diamond, Build then punches it at full force at the enemy, shredding the foe with its shards.
  • HawkGatling: Build spins the HawkGatlinger's ammo drum, increasing the number of shots fired by ten every time and projecting a sphere around him until he hits one hundred. Upon hitting one hundred he begins firing at everything caught within the sphere's radius.
  • NinninComic: Depending on what mode the 4Koma Ninpoutou is in, Build can perform the following: Clone Jutsu ^note  Build presses the Vortex Trigger one time and creates a number of clones of himself that attack together. , Fire Jutsu ^note  Build presses the Vortex Trigger two times and delivers a flaming slash attack. , Wind Jutsu ^note  Build presses the Vortex Trigger three times and creates a tornado around the blade. , and Stealth Jutsu ^note  Build presses the Vortex Trigger four times and teleports a short distance away in a puff of smoke. .
  • RocketPanda: Build fires up the Space Ride Arm and summons a white energy graph to wrap around the enemy, with him flying the trajectory of the graph while tearing them to shreds with Panda's claw at full force, repeatedly if needed.
  • FireHedgehog: Build extends Multi Deluge Gun on his Fire Engine arm into the enemy and fills them with water, then jumps and use his Hedgehog side's Spine Knuckle to pop them like a balloon.
  • LionCleaner: Build sucks an enemy in using the Long Range Cleaner until they are close enough to blast them with a lion-shaped energy blast from Lion's Gold Lio Gauntlet.
  • KeyDragon: Build traps his foe with chains from the Bind Master Key, then launches a powerful dark blue fireball.
  • KaizokuRessya: Build charges the Kaizoku Hassyar to its fourth tier, and fires a green energy train that rams into his foe, that also fires a series of blue discs.
  • OctopusLight: Build grabs his enemy with the tentacles on the Twist Lash Arm while blinding them with a rolling cloud of ink, then reels them in closer to use an electrified, blinding punch with his left hand.
  • RabbitTank Sparkling: In general it's an empowered kick. During its first outing, Build jumps high using Rabbit's foot, then summons a wormhole behind them to suck Blood Stalk's energy snakes in to trap them, then hits them with a powerful kick that then sends energy "bubbles" to bombard Stalk with enough for him to drop his transformation. Against Night Rogue, it was a more simple Dive Kick. Against Cross-Z, it's a simple back kick using Tank's foot.
  • PhoenixRobo: Flies using Phoenix's wings, he wreathes himself in flames and strike an enemy with Robot's hand repeatedly.
  • SmaphoWolf: Build summons Smartphone's application screen surrounding the enemy, then a virtual Wolf appears from the screen and attacks.
  • Black Hazard: It has two finishers:
    • Overflow: A dark energy-infused Rider Punch delivered either as a single blow, a series of rapid strikes, or a Touch of Death. When used as SmaphoWolf Hazard, the punch is accompanied by the image of a gigantic black wolf's head howling at the target. When used as HawkGatling Hazard, Build performs a series of blasts with the Hawk Gatlinger while flying around the enemy with the Sollstall Wings.
    • Hazard Finish: Build coats his right leg in purple dark energy before delivering a powerful kick. When used as HawkGatling Hazard, Build traps the enemy in a black cloud and performs a series of purple blasts with the Hawk Gatlinger.
  • RoseCopter: Build detaches the helicopter blade from his back, then covers it in red energy rose vines as it starts spinning before flying at the enemy for a slashing attack. An alternate version has Build instead grapple the enemy with Rose's vine whip before delivering an aerial shoulder tackle that shreds them with Helicopter's spinning blade.
  • KirinCyclone: Build summons an energy giraffe neck and attacks the enemy with it.
  • RabbitRabbit: Jumping into the air, Build stretches his leg towards the opponent, and pulling his body towards his foot, connects with the target, with the resulting impact sending his opponent flying.
  • TankTank: Build transforms his legs into tank treads, then launch a volley of bombardment from Fullbottle Buster Cannon Mode while circling the hapless foe.
  • Genius Form: It has three finishers:
    • Genius Attack: Build channels energy into the red, magenta, and orange parts of his body before delivering a punch covered in red energy. It's so powerful, it can even temporarily neutralize an opponent's Nebula Gas.
    • Genius Break: Build channels energy into the blue, cyan, and violet parts of his body before delivering a sidekick covered in blue energy that creates a shockwave upon impact and sends the enemy flying.
    • Genius Finish: Build channels energy into his entire body before performing an enhanced version of RabbitTank Form's Vortex Finish, with the graph being rainbow colored and Build emitting rainbow-colored gas in order to accelerate into the enemy. If used against a Lost Smash, he can remove the Nebula Gas inside said person without the risk of killing them. Adding the Hazard Trigger allows him to revert black Lost Bottles back into their original state.
  • In addition to these, the Drill Crusher has a different Vortex Break finisher for each of the 60 Fullbottles, normally some form of slash or thrust enhanced by the bottle's ability.
  • The FullBottle Buster has 60 different FullBottle Break finishers for each bottle, akin to the Vortex Break finishers of the Drill Crusher, but can additionally load more bottles in after the first to enhance the attack: Just Match Break for two, Miracle Match Break for three, and Ultimate Match Break for four. The Full Full RabbitTank Bottle, which is big enough to take up all four slots, performs the Full Full Match Break finisher when loaded, with its effects depending on Build's current form.
• Flash Step: Genius form can move at speeds that put RabbitRabbit to shame.
• Flight: Hawk (when it's used with Gatling, the wings are even larger), Rocket, Phoenix, Helicopter, Jet, and UFO's powers.
• Fragile Speedster: HawkGatling, NinninComic and KaizokuRessya all fall into this archetype, sacrificing strength and durability for increased speed relative to other Best Matches. All three happen to also rely on external equipment devised by Sento, making up for their lack of physical power through their weapons.
• Fusion Dance: Cross-ZBuild is him and Cross-Z merged into one.
• Gatling Good: The Gatling powers, and Sento developed the Hawkgatlinger to go with them.
• Gemstone Assault: Part of the Diamond powers involve creating diamond crystals and sending them at enemies. It can also be used to enhance defenses, as Rogue proves in their proxy battle.
• Glass Cannon: HawkGatling and KaizokuRessya make up for their low physical strength and complement their high speed with weapons that allow them to unleash immense firepower from a distance.
• Harmful Healing: Genius has the power to "heal" people of Nebula Gas affliction, potentially lowering their Hazard Levels (read:overall strength). Said treatment is often administered as a Rider Kick.
• Heroes Prefer Swords: Unusually for a Heisei Kamen Rider (aside for Gaim), he's got three sword-type weapons: the Drill Crusher, 4-Koma Ninpotou, and Fullbottle Buster. Various Fullbottles such as Lock or Helicopter grant swords or swordlike weapons of their own as a component of the suit.
• Highly-Visible Ninja: NinninComic is... bright purple and yellow.
• Hover Board: The UFO FullBottle gives him an energy variant.
• I Have Many Names: Thanks to Sento's modifications to the belt, the Build Driver makes a show of shouting out an Red Baron for each one of the thirty Best Matches and other forms he uses - even the ones not shown in the show.
• Jack of All Stats:
  • RabbitTank is the most well-rounded of the Best Matches, and also the most stable, proving compatible with enhancements that produce explosive results when used with others. That is why Build's upgrade forms are using RabbitTank as the base.
  • Many other Best Matches such as RocketPanda, LionCleaner, and SmaphoWolf are also portrayed as well-rounded, but have additional weapons and abilities that RabbitTank lacks. RabbitTank eventually sees its upgrades take the place of the new standard as the threats escalate.
• Light 'em Up: The Light Fullbottle has this ability. Also as a bit of Shock and Awe properties as well.
• Lightning Bruiser:
  • RabbitTank Sparkling gets to enjoy a brief tenure as one, before escalating threats render it simply the new baseline for a Jack of All Stats.
  • The Hazard Trigger turns any form into one of these regardless of its original characteristics. Between RabbitRabbit and TankTank, one emphasizes speed and the other power, but both are this trope relative to all of Build's earlier forms.
  • PhoenixRobo possesses the same flight and long-range capabilities as HawkGatling through its pyrokinesis, but unlike that form it also possesses enormous melee and defensive strength, making it the strongest of all the "vanilla" Best Matches.
• Luckily, My Shield Will Protect Me: The Smartphone FullBottle gives Build a shield. In the form of a giant smartphone.
• Making a Splash: Firetruck, Whale, and Pirate's powers.
• Master of None: Any of Build's mismatched Trial Forms. They don't necessary clash, it's just that their individual punching and kicking power are not as high as compared to their Best Matches. Zig-Zagged as the abilities of the halves of the Trial Forms can create forms tailor made for certain purposes, such as Firetruck and Whale Trial Form improves water-manipulating abilities of both sides.
• Mid-Season Upgrade: The Hazard Trigger allows Build to upgrade any Best Match into "Super Best Match" Hazard versions, which keep the eyes of the original forms but otherwise sport a sleek uniform black suit. RabbitTank Hazard can be further upgraded using the Full Full RabbitTank Bottle in place of the normal bottles to achieve two super forms, RabbitRabbit and TankTank.
• Mighty Glacier: GorillaMond and FireHedgehog fall into this category, sacrificing speed and mobility for superior physical power and durability. The former does this primarily through brute strength, the latter through abilities that make approaching Build to attack a near-impossibility.
• Multiform Balance: Build follows the Kamen Rider OOO model here, with specific combinations (Best Match) having the most optimized specialization and given more focus as the result.
• Oh, Crap!: The Build Driver has one whenever the Hazard Trigger is used. The last part of any Hazard form's transformation sequence is the Driver calling the thing uncontrollable and dangerous.

  Uncontrol Switch! Black Hazard! OH NO!

• Playing with Fire:
  • The Firetruck Fullbottle gives Build the ability to either shoot water or fire.
  • The Dragon Fullbottle gives Build this, but not to the extent that Cross-Z can use. Also the flames are blue.
  • The Phoenix Fullbottle also gives Build this ability as well.
• Power Fist:
  • The Gorilla powers give him the Muscle Glove, an oversized fist suited for strong punches.
  • The Robot FullBottle gives him a big robot fist on his left arm.
• Power Gives You Wings: Any use of Hawk or Phoenix FullBottles, for obvious reasons.
• Primary-Color Champion: His main form, RabbitTank, is primarily red and blue - with a dash of yellow on his belt.
• Restraining Bolt: The Full Full RabbitTank Bottle essentially acts as this for the Hazard Forms, as in addition to acting as a power up, it cancels out the corrupting nature of it.
• Rollerblade Good: The Tank half of Build's default form appropriately has tank treads on his sole that allow speedier movement or for a damage boost. TankTank adds larger treads to both of Build's knees that serve the same purpose.
• Rubber Man: RabbitRabbit, much like Maximum Mighty X before it, can elongate any of its limbs at will.
• Rule of Three: One needs a minimum Hazard Level of 3 if they have any hope of transforming using the Build Driver.
• Shoo Out the Clowns: Many of his goofier Best Matches such as OctopusLight and NinninComic are made permanently unavailable to him in the second half of the show after the panels containing them are attached to the Pandora Box. He later gets them back, but only briefly before they're taken again, and doesn't use them to transform during that time.
• Smug Super: While still present untransformed, Sento's more cocky and assured of himself while suited up.
• Spam Attack: Part of the terror of the Hazard Forms is that they spam finishers to devastating effect, usually in the form of breaking an opponent's defenses with an Overflow before attempting to murder them with a Hazard Finish.
• Spike Shooter: Hedgehog's powers, manifesting in the Spine Knuckle and Build Spine Shoulder pauldron. He can use it in the Drill Crusher Gun mode, which enables the weapon to shoot them.
• Spring Coil: The Rabbit half's leg is equipped with one for super jumping. Fittingly, the actual foot has a rabbit paw print as well, that is often imprinted on whatever Build walks on, even the Strong Smash in #1. In fact, Build's Rider Ability in Climax Fighters is his Rabbit Jump. RabbitRabbit adds coils to all four of Build's limbs to enable his new Rubber Man powers.
• Squishy Wizard: NinninComic and OctopusLight fall into this archetype. The former is a Fragile Speedster that lacks the Glass Cannon capabilities of the other high-speed Best Matches, but instead possesses a wide array of utility powers through its ninja techniques. The latter would be a Master of None if not for its abilities, which allow it to drown its opponent under hampering conditions with ink, light, and electrical shocks all delivered from a distance.
• Super Mode: Genius form.
• Superpowered Evil Side: The Hazard forms are much stronger than even RabbitTank Sparkling, but also turn him into an amoral berserker.
• Super-Speed: RabbitRabbit form allows Build to move at high speeds, allowing him to run faster and even dodge attacks.
• Super-Toughness: Diamond's abilities allow for this, in addition to summoning a storm of crystals.
• This Is a Drill: Build's Drill Crusher, which he uses as a sword and gun.
  • The Rhino Beetle (Kabutomushi) Fullbottle also equips one on his arm.
• Variant Power Copying: Build can steal his enemies' Nebula Gas Essences and save it for use later once purified, though the mechanics of how he uses the Essences are different. This likely has something to do with the purification process.
• Vine Tentacles: The Rose FullBottle gives him a thorn whip for long range attacks.
• Weapon Specialization: All of Build's forms can use any weapons summoned by the Build Driver, although some weapons are more effective when used by certain Best Match form. Due to being built by Sento himself rather than the weapons being formed by the suit, the weapons have been used a few times by Sento and Ryuga as themselves, without any visible drop in efficiency:
  • His default weapon is Drill Crusher, which has two modes: Sword and Gun.
  • The exclusive weapon of HawkGatling form is Hawk Gatlinger.
  • The exclusive weapon of NinninComic form is 4-Koma Ninpotou.
  • The exclusive weapon of KaizokuRessya form is the crossbow Kaizoku Hassyar.
  • RabbitRabbit and TankTank come with the Fullbottle Buster, a transformable weapon akin to the Drill Crusher on steroids. Unlike the former, this weapon is part cannon, not gun.
• Weapons That Suck: The Vacuum Cleaner (Soujiki) Fullbottle equips him with one, which is called the Long Range Cleaner.
• Wolverine Claws: Panda, Bear, Wolf, and Tiger each grant their own variant of this ability.
• Yellow/Purple Contrast: His Best Match NinninComic Form uses the Ninja and Comic halfbodies. The purple Ninja halfbody has the Onmitsu scarf that can wrap his entire body to camouflage himself with the local scenery, but the yellow Comic halfbody do the opposite with its flashiness when it creates highly visible Manga Effects when using its powers. The form's description as "Shinobi Entertainer" in its Transformation Name Announcement lampshades the contrast; a shinobi operates in concealment while an entertainer thrives in the spotlight.

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