History Characters / KamenRiderBuildProtagonists

* HybridPower: [[spoiler:Katsuragi, while studying Ryuga, determined that his unique genetics meant that his ever escalating Hazard Level might one day allow him to surpass Evolt in power. This eventually came through when he used the Muscle Galaxy Fullbottle to transfom into Cross-Z Evol, whose potential exceeds both Evolt and Killbus]].

* MismatchedEyes: Build's forms mostly have this, with them being different colors and shapes depending on what he uses for that side. Even the ones that are the same color seem to be different ''shades'' and are most definitely different ''shapes''. The only exceptions to this are [=RabbitRabbit=] and [=TankTank=], which deliberately use the same respective essence twice in each form.

* DidYouJustFlipOffCthulhu: He constantly delays Evolto's plans. As of #41, Evolto is so angry he promises that he won't kill Sento before crushing everything he has down to the last hope.

* GuileHero: When the situation calls for it, he has shown to have the capability of properly pulling off a BatmanGambit, even managing to OutGambit ''[[TheChessmaster Evolto]]'' on more than one occasion. [[spoiler:Most prominently at the end of the series.]]

** 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 Evolto 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.

* PhlebotinumRebel: Was one of the individuals who were captured and experimented by Faust, [[spoiler:or rather, his current personality was created by Evolto 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.]]

* SayMyName : '''EVOLTOOO!!!''' [[spoiler:Evolto sauntering on the scene as if nothing happened despite being in the middle of TheEndOfTheWorldAsWeKnowIt that he caused was just too much.]]

** Surprisingly enough though, he manages to ''[[InvertedTrope invert]]'' his status as this by turning [[spoiler:Evolto, [[DramaticIrony the main orchestrator of the events that occur in the series]], into HIS pawn by taking Evolto's gathered energies and using them to create a new world without the Sky Walls]].

* AmbiguouslyHuman: It's noted by several characters how odd his exponentially increasing Hazard Level is. [[spoiler:#30's {{Cliffhanger}} ends on the revelation that Banjo might not be human at all before #31 reveals that he's a HalfHumanHybrid due to Evolto's attempt to take control of his mother with the segment of his DNA that he sent back with the Mars Rover one month into her pregnancy.]]

* ApocalypseMaiden: [[spoiler:Blood Stalk's been grooming him since day one to be his, or rather Evolto's, vessel so he can have enough power to destroy the world with the Pandora Tower.]]

* ForWantOfANail: Actually a plot point in the finale. [[spoiler:Because the old world's Ryuga Banjo had Evolto's DNA in him, he technically counts as a different person (the second Ryuga Banjo from the new world has black hair, whereas the first one from the old world has his regular brown hair), and much like Sento, who doesn't have a counterpart, he retains his old memories]].

* HalfHumanHybrid: [[spoiler:His mother was infected by Evolto's body that hitched a ride back to Earth on Japan's first Mars Probe and the end result was Ryuga being born after ''two months'' and having an unknown alien genetic structure composing part of his genetic code, meaning he's a Human/Blood Tribe hybrid. Worth noting is this is so ingrained into him that Evolto actively trying to absorb all of the DNA needed for him to transform fails as Ryuga merely regenerates more.]]

* HybridPower: [[spoiler:Katsuragi, while studying Ryuga, determined that his unique genetics meant that his ever escalating Hazard Level might one day allow him to surpass Evolto in power. This eventually came through when he used the Muscle Galaxy Fullbottle to transfom into Cross-Z Evol, whose potential exceeds both Evolto and Killbus]].

* LukeIAmYourFather: [[spoiler:It's eventually revealed the alien that sired him was part of Evolto, meaning in essence, Evolto is his father. Evolto outright calls him "my spawn" after Ryuga manages to regenerate the DNA necessary for using his powers.]]

* SpannerInTheWorks: [[spoiler:Evolto's attempt to possess his mother instead resulted in the piece of him sent to Earth merging with Ryuga and making him a HalfHumanHybrid. Thus instead of having another half of him on Earth preparing the way for his arrival he could recombine with upon arrival, Evolto had to work a lot harder to become complete and ultimately ''can't'' strip Ryuga of his powers because Ryuga's body can just replace the DNA he stole.]]

** '''Blizzard Knuckle''': This variant of the Magma Knuckle instead uses a special '''Glacial Knuckle''' finishing move, which is similar to the '''Volcanic Knuckle''' but strong enough to damage Evolto in Black Hole form.

* GatheringSteam: How Ryuga’s rapidly increasing Hazard Level manifests. So long as he remains in Rider form and combat long enough while properly motivated, his power will continue to rise until he can overwhelm the opponent. This puts him in an interesting back and forth with Sento, as while Sento's upgrades give him an initial edge in strength, in every case Ryuga's rapid growth lets him close the gap by increasing his raw power. By the end of the system, Ryuga's Hazard Level passes 7, putting him on equal footing with Build Genius (the first time in years a secondary rider's final form hasn't been massively surpassed by the primary's. In fact he reached level 7 first.) and making him superior to every other rider in the series bar Evol Black Hole. Later, during his fight with Killbus (an opponent stronger than even Evol Black Hole), Evolto takes advantage of this by tricking him into rapidly elevating his Hazard Level. This allows him to transform into Cross-Z Evol, currently the strongest of the Build World rider forms and the first time in recent memory a secondary rider has eclipsed a primary rider's ultimate form.

* StoryBreakerPower: [=Cross-ZEvol=], which incorporates a fused Evolto, is as strong the ridiculously powerful Killbus - who can easily handle Cross-Z Magma (stronger than initial Evol Black Hole) and Evol Cobra in a two on one fight.

* KilledOffForReal: [[spoiler:He dies fighting Evolto's mimics in #47 and he goes down swinging.]]

* EleventhHourSuperpower: He gains Grease Blizzard during the final battle with Evolto, two episodes before the end of the series.

* BrokenFaceplate: [[spoiler:In #48, Gentoku as Rogue received a huge wallop from Evolto in his ultimate form, damaging his helmet's [[AllThereInTheManual Hard Jelly Eyes]].]]

* {{Determinator}}: Even when heavily outclassed by Evolto he still goes for a full assault in order to damage the latter's Evol Trigger. [[spoiler:A few punches and a [[FinishingMove Crack Up Finish]] later, he succeeded.]]

* DyingMomentOfAwesome: [[spoiler:Dies after going for a full assault towards Evolto in order to damage his Evol Trigger in #48. He succeeded at doing so, stunning Evolto and giving an opening for Sento and Ryuga to finish the rest.]]

* GoodCounterpart: To Utsumi. Both are Touto Government officials who are actually affiliated with Faust, and serve a father (or in Utsumi's case, a father figure). However, Gentoku is genuinely loyal to his father, and is willing to sacrifice his reputation to put the country in his father's hands, whereas Utsumi was willing to work with Namba's killer the second he had a chance. Furthermore, Gentoku's mental state improved drastically upon becoming a Kamen Rider, whereas Utsumi's...going to end up in a mental institution by the end of the series if he's lucky. And Gentoku is willing to do the right things in order to atone for his previous actions, while Utsumi is starting to do all sorts of wrong things and not feel any regret for his actions [[spoiler:(although it is later revealed that Utsumi was just pretending to join Evolto so that he could get revenge for Namba)]].

* HeelFaceTurn: #30-33 showcase his steady return back to his original kindhearted self, with his heightened Hazard Level thanks to the Sclash Driver having broken the spell the Pandora Box once held him under. And he now joins the heroes as one of the main Riders in the fight against Evolto.

** It turns out the conga line just stalled for a bit. For one, it turns out that raising his Hazard Level has also broken him free of the influence of the Pandora Box. While this does mean that he's good again, it also means that he has to bear the guilt of all of his sins. And he can't stop because Namba made sure to install an ExplosiveLeash onto him in order to force him into doing their bidding, up to forcing him to kidnap his father so that Evolto can have a bargaining tool to get back his Evol Driver. Then, when he finally finds a way to disable his kill chip, he ends up failing to stop Evolto, gets [[CurbStompBattle curb-stomped]] by Kamen Rider Evol's debut, and watches as Taizan ends up TakingTheBullet for him.

* TheShadowKnows: [[spoiler:When he finally dies fighting Evolto, he falls to his knees untransformed, wondering if he made his father proud even a little bit... but during the scene, his shadow is still the silhouette of Kamen Rider Rogue, showing that he did indeed go down a hero.]]

Prior to the show's events, Soichi was the astronaut who found Pandora Box on Mars 10 years ago and was subsequently possessed by the being known as Evolto. During the unveiling ceremony, Evolto touched the Box, attempting to destroy Earth as he had Mars but ended up initiating the Sky Wall Incident instead. Nine years later, he saved Misora from Faust, at which time he also stole a Pandora's Box panel, the Build Driver, and a number of Fullbottles. Soon after, Soichi encountered an amnesiac Sento in an alleyway and brought him in, encouraging him to use the Driver to become Kamen Rider Build. All of this was part of his schemes as [[Characters/KamenRiderBuildFaust Blood Stalk]], using Sento and Misora to gather all twenty Fullbottles as well as Pandora's Box and both panels for himself. He continues to play a role that alternates in equal parts between mentor and antagonist, raising Sento and Banjo's Hazard Levels in pursuit of his goals: the ultimate vessel and the ultimate Driver. Soon after completing Banjo's growth, Evolto gains the Evol Driver and Evolbottles to transform into Kamen Rider Evol.

For tropes pertaining to when Evolto's not pretending to be Soichi, see his entry under [[Characters/KamenRiderBuildFaust Blood Stalk]].

* AmbiguouslyHuman: At the end of #2, he twists a tablet computer into a back scratcher, and continues to demonstrate new abilities as the show progresses. Soichi claims his powers to be a result of having touched Pandora's Box on Mars, although that's not the whole story: his powers come from being possessed by Evolto.

* ConvenientComa: After Evolto leaves his body to possess Ryuga, Soichi is left alive, but unconscious for the time being.
* CordonBleughChef: His coffee is ''horrible''. Even he himself hates it! This takes a darker turn once you realize that [[DemonicPossession Evolto]] is an alien who has no clue how to make coffee and no reason to want to learn. [[spoiler:In the new world where Evolto never existed however, his coffee is ''[[SupremeChef amazing.]]'']]

* DemonicPossession: Ever since he went to Mars, Soichi has been possessed by Evolto, the destroyer of Mars who seeks to do the same to Earth.

* FightingFromTheInside: The reason so many of the Best Matches are so silly is because Soichi fought back against his demonic passenger when Evolto asked him "name 30 things you like", followed by [[KickTheDog "name 30 ways I could kill those things"]]. While at first his answers were things like tanks, gatling guns, rockets, and jets, once Soichi realized why Evolto was asking, he started providing random nonsense answers, and was able to do it for long enough that Evolto gave up and went with the silly bottles. He's also able to briefly wrest control of part of his body from Evolto, but never in a time or place where it particularly helps.

* MoralityPet: Misora is this to him, allegedly. In truth, she's only this to Soichi, not [[DemonicPossession Evolto]], who tries to kill her to kill Vernage.

** #30 reveals that he's been possessed by Evolto this whole time.

* WalkingSpoiler: As the BigBad of the show and a [[TheChessmaster chessmaster]] par excellence, it's impossible to talk about Soichi, or rather ''Evolto'', in any detail while pretending his early persona is all there is to him.

* SymbioticPossession: Misora's bracelet is capable of possessing her, turning her eyes a supernatural shade of green and causing her to display powers that allow her to tear down sections of the Sky Wall as well as easily defeat the Washio brothers and Kamen Rider Rogue. This possessed identity says nothing but the word "Evolto" in its first appearance, [[spoiler:but in its second introduces itself as Vernage, the queen of Mars, and subsequently explains that "Evolto" was the one who destroyed Mars with Pandora's Box]]. Misora doesn't mind, as the entity is protecting her and her friends, and never possesses her except when needed [[spoiler:unlike [[DemonicPossession her father's unwanted stowaway]].]] [[spoiler:As of #43 however, Vernage has been transferred to Ryuga to keep Evolto's DNA in check.]]

* RedemptionEarnsLife: [[spoiler:If she didn't she would have been just another statistic in Evolto's massive body count like the rest of the Namba faction.]]

* ArchEnemy: Is Evolto's. While she can't currently fight him on even footing, she's the reason he spent millions of years SealedEvilInACan and he's the reason she lost her entire planet and people.

* BigGood: Saves the heroes multiple times, gives them the means to control the Hazard Trigger's powers, and warns them of Evolto and actively opposes him at every turn. In fact, she's the reason the heroes managed to have a fighting chance against him ''at all'': she drained the bottles inside Pandora's Box so Evolto couldn't just open it and destroy Earth.

* DramaPreservingHandicap: At full power she was capable of fighting a fully empowered Evolto to a MutualKill, so if she were at full power the series would likely have been ''very'' short. All her powers are CastFromLifespan in her current state and thus have to be reserved for circumstances that only she can help with, and she can only emerge for very brief moments at a time.
* GoOutWithASmile: Once she senses that Sento's defeated Evolto for good, she possesses Misora one last time to remark on it and then releases the bracelet's clasp and passes on with a smile on her face.

* PhysicalGod: Her first display of power terrifies Seito enough that they fall back for the time being out of sheer fear of her. At full power she was capable of taking on full power Evolto one on one and fighting him to a draw.
* PyrrhicVictory: Vernage eventually managed to defeat a fully powered Evolto, but by the time she managed to do so, he had already wiped out the rest of the Martians and destroyed what was left of their civilization. Downplayed, however, as it still trapped him on Mars for millions of years and likely saved a lot of planets from being destroyed by him in the process.
** Evolto and Shinobu tried to invoke this by turning her host, Misora, into the CD Lost Smash, as due to Vernage's power not even Genius Form could save her host from death. Sento bypassed this by using Genius Form's abilities to kick Misora into Ryuga and transfer Vernage to him so she'd survive.
* SpannerInTheWorks: She's ultimately the biggest roadblock to Evolto's plans. If she didn't defeat Evolto all those years ago, he would have just continued his planet destroying spree. And if she didn't follow him to Earth and drain out the Fullbottle essences from the Pandora Box, Evolto would have won the second he touched the Box instead of just the Skywalls forming (not to mention that it means the heroes still have Fullbottles to fight back with after Evolto uses them to create the Evol Trigger).
* SymbioticPossession: Unlike Evolto, she's genuinely benevolent and heroic and Misora is very willing to have her around. She's saved everyone on multiple occasions.

* WorfHadTheFlu: The only reason she's unable to finish off Evolto herself is that her SoulJar isn't able to sustain her indefinitely and her powers are gradually weakening. At her full power, she was able to fight a fully powered Evolto to a MutualKill and total the Evol Driver, leaving him stranded on Mars for millions of years.

* EmptyShell: Sento's first use of the Hazard Trigger leaves him so horrified by [[MyGodWhatHaveIDone what he proceeds to do under its influence]] that he's left a depressed wreck. To accentuate this point, in episode 21, most times when his face is shown, his eyes are framed in such a way that they look [[EmptyEyes completely black]].

* HeroicBSOD: When Sento encounters a source of emotional distress too great to deflect, he tends to shut down entirely. Episodes 16 and 21 feature prominent examples.

* HesBack: Pulls this off twice through-out the entire series, once in episode 16 after a pep-talk from Banjo. [[spoiler: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 [[SuperMode Build Genius Form]] for the first time.]]

* NotWorthKilling: After they steal all the Fullbottles he had on his person at the end of episode 10, Night Rogue and Blood Stalk opt to leave him wounded in the dirt instead of finishing him off. [[spoiler:They still need him to purify the remaining Fullbottles and finish the Sclash Driver, after all.]]
* PerpetualFrowner: The events from episode 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.

* QuestForIdentity: 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 RedHerring is floated before episode 15 finally reveals his true identity: [[spoiler: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.

* UnwittingPawn: Most of Sento's actions prior to episode 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.

* AllYourPowersCombined: [[spoiler:Genius Form lets him access the power of all 60 Fullbottles at will. This is first seen in episode 42 where Build is able to use the Diamond Fullbottle's shielding powers to defend against Evol's Steam Attack.]]

** Sento also used the Beat Closer when using [=KeyDragon=] Hazard Form in episode 35.

* SpringCoil: 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 ''episode 1''. In fact, Build's Rider Ability in ''[[VideoGame/KamenRiderClimaxHeroes Climax Fighters]]'' is his [[InASingleBound Rabbit Jump]]. [=RabbitRabbit=] adds coils to all four of Build's limbs to enable his new RubberMan powers.

* {{Hypocrite}}: In episode 5, he says (paraphrased) "Sento is so selfish for focusing on his own problems... he should be focusing on '''my''' problems!" This doesn't qualify as HypocriticalHumor because [[spoiler:there's nothing funny about him knocking out Sento and turning the VictimOfTheWeek back into a Smash in the hopes that it'll lead him to Faust's base.]]

* GatheringSteam: How Ryuga’s rapidly increasing Hazard Level manifests. So long as he remains in Rider form and combat long enough while properly motivated, his power will continue to rise until he can overwhelm the opponent. This puts him in an interesting back and forth with Sento, as while Sento's upgrades give him an initial edge in strength, in every case Ryuga's rapid growth lets him close the gap by increasing his raw power. By the end of the system, Ryuga's Hazard Level passes 7, putting him on equal footing with Build Genius (the first time in years a secondary rider's final form hasn't been massively surpassed by the primary's. In fact he reached level 7 first.) and making him superior to every other rider in the series bar Evol Black Hole. Later, during his fight with Kilbas (an opponent stronger than even Evol Black Hole), Evolto takes advantage of this by tricking him into rapidly elevating his hazard level. This allows him to transform into Cross-Z Evol, currently the strongest of the Build World rider forms and the first time in recent memory a secondary rider has eclipsed a primary rider's ultimate form.

* StoryBreakerPower: [=Cross-ZEvol=], which incorporates a fused Evolt, is as strong the ridiculously powerful Kilbus- who can easily handle Cross-Z Magma (stronger than initial Evol Black Hole) and Evol Cobra in a two on one fight.

* UnskilledButStrong: Compared to Sento, Ryuga is a brutish fighter and lacks access to Build's wide array of situational tricks. However, his Hazard Level grows at an unrivaled rate, surpassing Sento's by episode 19 despite Sento having far more experience. Such is Ryuga's rate of advancement, in fact, that several other characters know they're on a fairly strict time limit to defeat him before they no longer can.

* TheCameo: He debuts after ''[[Film/KamenRiderHeiseiGenerationsFinalBuildAndExAidWithLegendRiders Heisei Generations Final: Build & Ex-Aid with Legend Riders]]'', which chronologically takes place after episode 14 and before his introduction in the series. During the movie, he steals the Phoenix and Robot Fullbottles from Build. In the series, he appears for a brief moment defeating Guardians at the end of episode 16.

* DeadlyUpgrade: Kazumi starts ''chaining'' them in the show's last act, with two separate Nebula Gas infusions in episodes 40 and 44, followed by using the Blizzard Knuckle with the Build Driver in episode 46 to acquire the Grease Blizzard form, ''all of which'' have the potential to kill him. Sento even says that if he uses Grease Blizzard with his elevated Hazard Level, it'll almost certainly kill him. [[spoiler:And it does. Thankfully, the world reset seems to have fixed this problem and thus he's able to use Grease Blizzard without issue.]]

* EleventhHourSuperpower: He gains Grease Blizzard during the final battle with Evolt, two episodes before the end of the series.

* TheJuggernaut: In Episode 22, it was shown that Grease, unlike Cross-Z Charge or Build, is ''extremely'' durable, and was able to take attacks continuously from a variety of Best Match forms and finishing moves, and didn't seem worse for wear. The only reason he apparently lost was due to Sento using the Hazard Trigger, but even ''that'' lasted until ''nightfall'', and it was only when Sento [[SuperPoweredEvilSide lost control]] and whipped out the big guns that Grease was forced out of his transformation.

* EvenEvilHasLovedOnes: He's genuinely worried when his father suffers a major heart attack during the tenth episode, but that is immediately superseded by how giddy he is that this happenstance makes him the de facto leader of Touto. This can also be seen as his original kinder nature briefly pushing through what the Pandora Box's HatePlague did to him.

* HeelFaceTurn: Episodes 30 through 33 showcase his steady return back to his original kindhearted self, with his heightened Hazard Level thanks to the Sclash Driver having broken the spell the Pandora Box once held him under. And he now joins the heroes as one of the main Riders in the fight against Evolto.

** It turns out the conga line just stalled for a bit. For one, it turns out that raising his Hazard Level has also broken him free of the influence of the Pandora Box. While this does mean that he's good again, it also means that he has to bear the guilt of all of his sins. And he can't stop because Namba made sure to install an ExplosiveLeash onto him in order to force him into doing their bidding, up to forcing him to kidnap his father so that Evolto can have a bargaining tool to get back his Evol Driver. Then, when he finally finds a way to disable his kill chip, he ends up failing to stop Evolt, gets [[CurbStompBattle curb-stomped]] by Kamen Rider Evol's debut, and watches as Taizan ends up TakingTheBullet for him.

** Episodes 13 and 14 reveal that he's Blood Stalk and has been manipulating the group the entire time. When Misora wouldn't/couldn't purify Bottles for Faust any more, he "rescued" her and set Sento up as her heroic guardian to get her back on the job. Also, he works for Namba now.
** Episode 30 reveals that he's been possessed by Evolto this whole time.

* HealingHands: Develops this power in episode 19. It comes with the same restrictions as purifying Fullbottles, namely exhaustion.

* LockedOutOfTheLoop: Sento and Ryuga try to pull this on her in episode 14 regarding Blood Stalk's identity, only for her to figure it out by herself in the end of the next episode.

* SocialMediaBeforeReason: Deliberately invokes this with the Needle Smash in the first episode to prompt Sento to save her, giving her an excuse to infiltrate nascita.

* WorfHadTheFlu: The only reason she's unable to finish off Evolto herself is that her SoulJar isn't able to sustain her indefinitely and her powers are gradually weakening. At her full power she was able to fight a fully powered Evolto to a MutualKill and total the Evol Driver, leaving him stranded on Mars for millions of years.

* NotSoDifferent: To a ''disturbing'' level with Takumi Katsuragi, from the high IQ and hairdo, to his taste in food. So close, in fact, that [[spoiler:they're the same person]].

* NotSoDifferent: As of #34, the reveal of Ryuga's origin [[spoiler:as an amnesiac part of [[BigBad Evolto]]'s other half makes him no different to Sento and his past life as [[MadScientist Takumi Katsuragi]]]].

--> '''Kazumi''': [[NotSoDifferent You can probably burn for the same reason our passions do.]]
* EvilKnockOff: Though "evil" is a rather strong word. Like Sento, he's lost all his memories of his previous life and similar to Banjo, he enjoys a good fight. To further the parallels, he was handpicked by Blood Stalk to be a Kamen Rider, just like they were. This crosses into NotSoDifferent as Kazumi cares about the Trio in a similar stand-offish way that Sento and Ryuga do about each other. He is more violent with his AngerBornOfWorry, though.

!!nascita

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

* CharacterTics: [[spoiler: [[ParentsKnowTheirChildren As noted by his father,]]]] Sento makes the habit of messing with his hair whenever he is anxious, upset, or excited.

* GuileHero: When the situation calls for it, he has shown to have the capability of properly pulling off a BatmanGambit, even managing to OutGambit ''[[TheChessmaster Evolto]]'' on more than one occasion. [[spoiler: Most prominently at the end of the series.]]

* HeroicWillpower: [[spoiler: Manages to resist Tid's mind control in ''Heisei Generations Forever''.]]

* {{Irony}}: [[spoiler: 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.]]

** 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 ThouShaltNotKill attitude and [[spoiler: Katsuragi's new life as Sento.]]

* NotSoDifferent: To a ''disturbing'' level with Takumi Katsuragi, from the high IQ and hairdo, to his taste in food. So close, in fact, that [[spoiler: they're the same person]].

* EvilKnockoff: [[spoiler: The Build Driver is actually a ''good'', though still lesser, knockoff of the Evol Driver.]]

*** '''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. [[spoiler: Adding the Hazard Trigger allows him to revert black Lost Bottles back into their original state.]]

!!!Portrayed by: Eiji Akaso (live), Eitoku (suit)

* AntiHero -> TheHero: Ryuga starts the show with decidedly selfish motivations for fighting against Faust, but steadily begins to mature through seeing Sento's heroism in action. It's not until he grows past his antiheroic status that he can become a Kamen Rider in his own right. Eventually, he becomes a straight up hero and essentially cites Sento as his role model. [[spoiler: This is concluded by him trying to sacrifice himself in the final battle while repeating Sento's speech from [[Recap/KamenRiderBuildEp3BorderlineOfJustice #3]].]]

** EmpoweredBadassNormal: Even before the infusions, Ryuga was a talented boxer. [[spoiler: Due to being half-Blood Tribe, he was actually this ''from the moment he was born''.]]

* TraumaCongaLine: He loses his career trying to get money for his girlfriend's operation, gets framed for murder [[spoiler: because said girlfriend was tricked into sending him there]], gets abducted from prison and used as a guinea pig for horrific experiments, escapes only to be treated as a fugitive from the government and sees his girlfriend turned into a Smash and die in his arms because her body was too weak to survive being turned back into a human. That's just the first two episodes. Ryuga has it tough.

* WreckedWeapon: His Sclash Driver gets destroyed when he [[TakingTheBullet uses his own body as a shield]] to defend [[spoiler: Vernage]] from Stalk.

!!!Portrayed by: Kouhei Takeda (live), Satoshi Fujita (suit)

* AmnesiacDissonance: The loss of his memories turned him from a kindhearted farmer to a PsychopathicManchild with an odd obsession with internet idols. [[spoiler: Subverted in that he was faking, and trying unsuccessfully to alienate the Three Crows so that they wouldn't follow him to their deaths.]]

* ConditionedToAcceptHorror: #21 gives a reason for why Kazumi is coldly professional when it comes to everything else but fighting. He has seen people die in front of him already and is accustomed to the harsh reality of the war he is a weapon of. His not-so-visible [[NotSoStoic reaction]] to [[spoiler: Aoba's death]] shows that it's not complete.

* KilledOffForReal: [[spoiler: He dies fighting Evolt's mimics in #47 and he goes down swinging.]]

* CantCatchUp: Grease spends most of the middle half of the show lagging badly behind everyone else, with all of Seito's forces being as strong as him or stronger. In the last quarter, aware of his status as the weakest of the four main Riders, he starts taking increasingly desperate measures to avert this. [[spoiler: It somewhat backfires on him, as his drastic measures rendered the actual upgrade Sento had been building for him a fatal one if used]].

* DeadlyUpgrade: Kazumi starts ''chaining'' them in the show's last act, with two separate Nebula Gas infusions in episodes 40 and 44, followed by using the Blizzard Knuckle with the Build Driver in episode 46 to acquire the Grease Blizzard form, ''all of which'' have the potential to kill him. Sento even says that if he uses Grease Blizzard with his elevated Hazard Level, it'll almost certainly kill him. [[spoiler: And it does. Thankfully, the world reset seems to have fixed this problem and thus he's able to use Grease Blizzard without issue.]]
* DualWielding: [[spoiler: He eventually gets a second Twin Breaker, which blends well with his upgraded Hazard Level.]]

* MotifMerger: [[spoiler: As Grease Blizzard, at least his right shoulder armor is adorned with the symbols of the Castle, Stag, and Owl [=FullBottles=], the latter two in the foreground]].[[spoiler:Grease Perfect Kingdom also takes the designs and the armaments of the Three Hokuto Crows into a single suit]]

** Played straight as [[spoiler: Grease Blizzard, which clearly could take a beating from the Hokuto Crow mimics. Kazumi only died because the Knuckle pushed him ''way too far'' past his limit. After the World Reset, that problem is taken care of and it's the first thing that's actually able to put a dent in Metal Build, who's himself this trope, and even withstands a finisher from him without losing transformation. It takes a finisher and being thrown out a skyscraper by the ''much'' stronger Phantom Build to knock him out of transformation, and even then he ''survives'' and is still in fighting shape once he upgrades to the even stronger Perfect Kingdom.]]

!!!Portrayed by: Kensei Mikami (live), Jun Watanabe (suit)

* UsedToBeASweetKid: According to his father, he used to a gentle kid before the Sky Wall Incident. This is also one of the reasons why his father refused to think about how much Gentoku changed in the following years up until early into the story. [[spoiler: After his HeelFaceTurn we get to see that Gentoku in his normal state is a lovable goofball with [[RummageSaleReject horrendous fashion sense]] proving his father right.]]

!! Tropes exclusive to him as Kamen Rider Rogue

!!!Portrayed by: Yasuyuki Maekawa (live), Tetsuo Kanao (voice)

!!!Portrayed by: Kaho Takada (live), [[spoiler:Creator/SoraAmamiya (voice only, as Vernage)]]

* SymbioticPossession: Misora's bracelet is capable of possessing her, turning her eyes a supernatural shade of green and causing her to display powers that allow her to tear down sections of the Sky Wall as well as easily defeat the Washio brothers and Kamen Rider Rogue. This possessed identity says nothing but the word "Evolto" in its first appearance, [[spoiler:but in its second introduces itself as Vernage, the queen of Mars, and subsequently explains that "Evolto" was the one who destroyed Mars with Pandora's Box]]. Misora doesn't mind, as the entity is protecting her and her friends, and never possesses her except when needed [[spoiler:unlike [[DemonicPossession her father's unwanted stowaway]].]] [[spoiler: As of #43 however, Vernage has been transferred to Ryuga to keep Evolto's DNA in check.]]

!!!Portrayed by: Yukari Taki

* BecomingTheMask: [[spoiler: This is the crux of her ''actual'' HeelFaceTurn. Turns out when you give someone a family, and genuine affection that they didn't get as a child, they grow attached to both. Guess Juzaburo Namba isn't as smart as he thought.]]

* IntrepidReporter: Tries to uncover the mystery around Smash and Kamen Rider. Her first reaction after seeing a Smash is to try and take a picture of it. Unfortunately, this put her life at risk in the process. [[spoiler: This takes a darker turn once you learn that she's one of the Namba Children.]]

* YouHaveOutlivedYourUsefulness: Faust turns her into a Smash after her cover is blown. Once she recovers, she switches sides. [[spoiler: At least that's what it's supposed to look like... and it is!]]

!!!Voiced by: Creator/SoraAmamiya

* DarkestHour: [[spoiler:Sento's occurs not during the series, but in ''[[Film/KamenRiderBuildBeTheOne 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 Banjou, the BigBad 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: [[TrueCompanions his bond with Banjo]], and his father's belief in [[ArcWords Love and Peace]], which gives him the resolve to keep fighting and save the world.]]

* MeaningfulName: 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 episode 9, where Ryuga raises the point, Soichi explains the name and Sento incredulously shouts, "So you just named me ''[=RabbitTank=]''?!"

* HybridPower: [[spoiler:Katsuragi, while studying Ryuga, determined that his unique genetics meant that his ever escalating Hazard Level might one day allow him to surpass Evolt in power. This eventually came through when he used the Muscle Galaxy Fullbottle to transfom into Cross-Z Evol, whose potential exceeds both Evolt and Kilbas]].

* SpannerInTheWorks: [[spoiler:Evolto's attempt to possess his mother instead resulted in the piece of him sent to Earth merging with Ryuga and making him a HalfHumanHybrid. Thus instead of having another half of him on Earth preparing the way for his arrival he could recombine with upon arrival, Evolt had to work a lot harder to become complete and ultimately ''can't'' strip Ryuga of his powers because Ryuga's body can just replace the DNA he stole.]]

* DeadlyUpgrade: The Sclash Driver draws its overwhelming power from exposing the user to the raw, unfiltered effects of Nebula Gas, which has the same effects on the user's personality as being near the Pandora Box when it was activated. Even the first usage causes Banjo to take on a berserker's fighting style and adds a menacing growl to his voice while wearing the suit, and repeated usage will turn the user into a BloodKnight who can think of nothing but battle. Making matters worse, its mental stresses come with accompanying physical stresses, enough so that just the act of transforming with it for the first time is an agonizing experience and prolonged battle will often see Banjou be overwhelmed by the strain. It takes six episodes of frequent usage for Banjou to finally acquire an immunity to the physical stresses of the Driver.

* EvilSoundsDeep: Wearing the Sclash Driver makes Banjou dramatically more aggressive than he is normally, and gives his voice a rough growl to match.

*** The Rider Kick version: Banjou summons a blue and orange energy Chinese dragon that flies behind him, then he jumps up as the dragon breaths fire, with said fire pushes Banjou to the enemy, then he delivers a roundhouse kick whilst his foot is covered in blue energy (basically a combination of [[Series/KamenRiderRyuki Ryuki/Ryuga's]] Final Vent (the dragon summoning and the push) and [[Series/KamenRiderKabuto Gatack's]] Rider Kick (the jumping roundhouse kick)).
*** The Rider Punch version: Banjou charges up a blue Chinese dragon-shaped energy in his right hand before delivering a punch to the victim.
** '''Beat Closer''': It has three finishers, all of which are delivered by a powerful Rider Slash. The 3 finishers are determined by how many times Banjou pulls the handle, and if a Fullbottle is inserted in the hilt, which increases their power: '''Smash Hit''' (pulls handle once), '''Million Hit''' (pulls handle twice), and '''Mega Hit''' ([[RuleOfThree pulls handle thrice]]). All three become "Slash"es when the Beat Closer is augmented by inserting a Fullbottle.

** '''Cross-Z Magma''': Banjou's SuperMode has the '''Volcanic Attack''', a bog-standard Rider Kick with the twist of forming dragons of magma around him that allow him to melt through anything in his way before surrounding him during his downwards descent to counter incoming projectiles and to give his kick a red-hot explosive enhancement. And his second move is '''Volcanic Finish''', where Cross-Z performs a [[RapidFireFisticuffs series of rapid flaming punches]] before delivering a volcanic final punch.

** '''Blizzard Knuckle''': This variant of the Magma Knuckle instead uses a special '''Glacial Knuckle''' finishing move, which is similar to the '''Volcanic Knuckle''' but strong enough to damage Evolt in Black Hole form.

* GatheringSteam: How Ryuga’s rapidly increasing Hazard Level manifests. So long as he remains in Rider form and combat long enough while properly motivated, his power will continue to rise until he can overwhelm the opponent. This puts him in an interesting back and forth with Sento, as while Sento's upgrades give him an initial edge in strength, in every case Ryuga's rapid growth lets him close the gap by increasing his raw power. By the end of the system, Ryuga's Hazard Level passes 7, putting him on equal footing with Build Genius (the first time in years a secondary rider's final form hasn't been massively surpassed by the primary's. In fact he reached level 7 first.) and making him superior to every other rider in the series bar Evol Black Hole. Later, during his fight with Kilbas (an opponent stronger than even Evol Black Hole), Evolt takes advantage of this by tricking him into rapidly elevating his hazard level. This allows him to transform into Cross-Z Evol, currently the strongest of the Build World rider forms and the first time in recent memory a secondary rider has eclipsed a primary rider's ultimate form.

* LightningBruiser: Cross-Z Magma is a gigantic upgrade over Cross-Z Charge in every aspect, towering over [=RabbitRabbit=] and [=TankTank=] for raw physical prowess. With Banjou's ever-escalating Hazard Level surpassing any normal human's limitations, Magma soon becomes so powerful that it can even stand up to Evol and Genius.

** Banjou gained a second SuperMode using the Muscle Galaxy Full Bottle to turn into Cross-Z Evol.

* WhenAllYouHaveIsAHammer: Since Sento hoards most of their [=FullBottles=], Banjo typically only has access to the Dragon and Lock combo components, if he even has those. Without his partner's diversity of options, Banjo has just one tactic in battle: to punch his problems harder and force his Hazard Level to rise until he can overwhelm his opponent with brute force. That said, he relies on this tactic for a good reason: ''it always works''. No matter how desperate the situation, Banjou can accomplish seemingly impossible feats through sheer grit and willpower.

* DyingMomentOfAwesome: [[spoiler:Dies after going for a full assault towards Evolto in order to damage his Evol Trigger in #48. He succeeded at doing so, stunning Evolt and giving an opening for Sento and Ryuga to finish the rest.]]

* TookALevelInBadass: He mops the floor with all three previous Riders after becoming Kamen Rider Rogue. The upgrade improves not just his physical performance, but also his skills as a tactician, as he's able to casually turn [=RabbitTank=] Hazard's berserker traits to his advantage. He's even the first person to force Blood Stalk to drop his transformation, although not before Banjou softened him up beforehand.

* DramaPreservingHandicap: At full power she was capable of fighting a fully empowered Evolt to a MutualKill, so if she were at full power the series would likely have been ''very'' short. All her powers are CastFromLifespan in her current state and thus have to be reserved for circumstances that only she can help with, and she can only emerge for very brief moments at a time.

* PhysicalGod: Her first display of power terrifies Seito enough that they fall back for the time being out of sheer fear of her. At full power she was capable of taking on full power Evolt one on one and fighting him to a draw.

* ContrastingSequelProtagonist: Sento is obviously more acerbic than his predecessor Emu, 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 InsufferableGenius nature and created their own belts and weaponry, with the difference being that Sento is genuinely heroic where Kuroto is a HeroicComedicSociopath at the best of times.

* GuileHero: When the situation calls for it, he has shown to have the capability of properly pulling off a BatmanGambit, even managing to OutGambit ''[[TheChessmaster Evolt]]'' on more than one occasion. [[spoiler: Most prominently at the end of the series.]]

* AmnesiacDissonance: Acknowledging it is part of Sento overcoming his HeroicBSOD in episode 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.
** [[spoiler: 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.]]

* AntiHero: Implied: His premiere appearance in ''Series/KamenRiderExAid'', had him show up to take a sample of Emu's essence and then, in contrast to how new and old MainCharacters would briefly team-up during the finale of the current series, leaving the heroes to deal with the pandemic themselves. [[spoiler: 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.]]

* BashBrothers: 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 BokeAndTsukkomiRoutine, 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.

* RedOniBlueOni: The blue to Banjo's red
* DarkestHour: [[spoiler:Sento's occurs not during the series, but in ''[[Film/KamenRiderBuildBeTheOne Be The One]]''. He's been completely isolated by the Blood Race, who brainwashed all of Japan (including Banjou, Misora, and Sawa) into hating Build, and captured Kazumi and Gentoku since they can't be brainwashed. After being defeated by Banjou, the BigBad 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: [[TrueCompanions his bond with Banjou]], and his father's belief in [[ArcWords Love and Peace]], which gives him the resolve to keep fighting and save the world.]]

* DidYouJustFlipOffCthulhu: 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.

* HesBack: Pulls this off twice through-out the entire series, once in episode 16 after a pep-talk from Banjo. [[spoiler: 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 [[SuperMode Build Genius Form]] for the first time.]]

* {{Irony}}: [[spoiler: 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 Killbas 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.]]

** 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.

* PhlebotinumRebel: Was one of the individuals who were captured and experimented by Faust, [[spoiler: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.]]

* SayMyName : '''EVOLT!!!''' [[spoiler: Evolt sauntering on the scene as if nothing happened despite being in the middle of TheEndOfTheWorldAsWeKnowIt that he caused was just too much.]]

** Surprisingly enough though, he manages to ''[[InvertedTrope invert]]'' his status as this by turning [[spoiler: Evolt, [[DramaticIrony 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]].

* AmbiguouslyHuman: It's noted by several characters how odd his exponentially increasing Hazard Level is. [[spoiler: #30's {{Cliffhanger}} ends on the revelation that Banjo might not be human at all before #31 reveals that he's a HalfHumanHybrid due to Evolt's attempt to take control of his mother with the segment of his DNA that he sent back with the Mars Rover one month into her pregnancy.]]

* RedOniBlueOni: The red to Sento's blue
* ApocalypseMaiden: [[spoiler: Blood Stalk's been grooming him since day one to be his, or rather Evolt's, vessel so he can have enough power to destroy the world with the Pandora Tower.]]

* BetterThanNew: In Episode 30 Stalk blasts Ryuga with his Martian energy powers, destroying the Dragon Sclashjelly. However, the blast causes the gel inside the packet to harden into a rock-like substance, which eventually breaks open to reveal the Dragon Magma Fullbottle, giving Ryuga a new form that's far stronger than Cross-Z Charge.

* ForWantOfANail: Actually a plot point in the finale. [[spoiler: Because the old world's Ryuga Banjou had Evolt's DNA in him, he technically counts as a different person (the second Ryuga Banjou from the new world has black hair, whereas the first one from the old world has his regular brown hair), and much like Sento, who doesn't have a counterpart, he retains his old memories]].

* HalfHumanHybrid: [[spoiler:His mother was infected by Evolt's body that hitched a ride back to Earth on Japan's first Mars Probe and the end result was Ryuga being born after ''two months'' and having an unknown alien genetic structure composing part of his genetic code, meaning he's a Human/Blood Tribe hybrid. Worth noting is this is so ingrained into him that Evolt actively trying to absorb all of the DNA needed for him to transform fails as Ryuga merely regenerates more.]]

* HiddenDepths: In spite of his DumbMuscle status, he can still put two and two together at times and play the 'common sense' to Sento. He immediately figures out that Best Matches follow an Biotic + Abiotic formula, something Sento [[YouWereTryingTooHard had overlooked as too obvious to possibly be the solution.]]

* LukeIAmYourFather: [[spoiler:It's eventually revealed the alien that sired him was part of Evolt, meaning in essence, Evolt is his father. Evolt outright calls him "my spawn" after Ryuga manages to regenerate the DNA necessary for using his powers.]]

* NotSoDifferent: As of episode 34, the reveal of Ryuga's origin [[spoiler:as an amnesiac part of [[BigBad Evolt]]'s other half makes him no different to Sento and his past life as [[MadScientist Takumi Katsuragi]]]].

* SpannerInTheWorks: [[spoiler:Evolt's attempt to possess his mother instead resulted in the piece of him sent to Earth merging with Ryuga and making him a HalfHumanHybrid. Thus instead of having another half of him on Earth preparing the way for his arrival he could recombine with upon arrival, Evolt had to work a lot harder to become complete and ultimately ''can't'' strip Ryuga of his powers because Ryuga's body can just replace the DNA he stole.]]

* UnlimitedWardrobe: In contrast to Sento's one outfit, Ryuga has new clothes every other episode. On the other hand, these clothes are often more or less ridiculous disguises that Souichi or Misora whipped up.

* AffectionateNickname: [[ParodiedTrope Parodied]]. After joining the Touto riders, he's insistent on at least Ryuga calling him "Kazumin". Also played straight in his insistence on calling Misora by her Idol name Mii-tan despite now knowing her ''actual'' name.

** Later on, he and [[spoiler: Gentoku]] form a similar duo as Sento and Ryuga. Interestingly enough, Kazumi is usually the sane one of them two.

* DiedInYourArmsTonight: [[spoiler: Misora holds him as he is dying in #47.]]

* FirstNameBasis: He's the only member of Team Build to refer to Banjou as Ryuga.
* GoodAngelBadAngel In Episode 46, he sees Misora's towel draped across the back of a chair and mentally debates using it to dab the sweat off his face. His good angel (depicted as Kazumi in chains) says that if he sinks that low he has no right to call himself an idol fan, while his bad angel (Kazumi in summer clothing sitting in a deck chair with the Mii-tan body pillow) says that she shouldn't have left it there if she didn't want people using it. His bad side wins...[[spoiler:and then it turns out to be ''Gentoku's'' towel rather than Misora's.]]

* NiceJobBreakingItHero: Sento originally made the Blizzard Knuckle as a safe power-up for him, to increase his Hazard Level to manageable levels. However in his own hastiness to get stronger he runs off to get additional doses of Nebula Gas TWICE before it could be given to him. By the time he receives the Knuckle, it was too late as the additional power it provides would now be too much for his body to handle, [[spoiler: resulting in his own death after he eventually gets forced to use it to transform]].

* AmbiguouslyEvil: In his earliest appearances, where he's obviously sinister but allegedly working for a good cause. It doesn't take long for his true nature to come out, and the trailer at the end of episode 6 makes obvious what episode 7 confirms: he's Night Rogue, and his evil is anything but ambiguous. [[spoiler:This trope is reapplied when he becomes Kamen Rider Rogue until his true intentions are later revealed.]]

* BrokenFaceplate: [[spoiler: In episode 48, Gentoku as Rogue received a huge wallop from Evolt in his ultimate form, damaging his helmet's [[AllThereInTheManual Hard Jelly Eyes]].]]

* {{Determinator}}: Even when heavily outclassed by Evolt he still goes for a full assault in order to damage the latter's Evol Trigger. [[spoiler:A few punches and a [[FinishingMove Crack Up Finish]] later, he succeeded.]]

* DyingMomentOfAwesome: [[spoiler:Dies after going for a full assault towards Evolt in order to damage his Evol Trigger in episode 48. He succeeded at doing so, stunning Evolt and giving an opening for Sento and Ryuga to finish the rest.]]

** During #31 he uses a grapple with Sento to secretly explain that Midou is actually Namba in disguise and that he only wanted to use Pandora's Box as a deterrent while Namba has more sinister plans for it, imploring him to steal the box before it can be opened. He tellingly even checks during the grapple several times to see if either of the fanatically loyal to Naba Kaisers can hear him.

* FirstEpisodeTwist: The end of episode 6 reveals his identity as Night Rogue after considerable teasing beforehand. It becomes impossible to talk about Gentoku's further actions without mentioning it.

* GoodCounterpart: To Utsumi. Both are Touto Government officials who are actually affiliated with Faust, and serve a father (or in Utsumi's case, a father figure). However, Gentoku is genuinely loyal to his father, and is willing to sacrifice his reputation to put the country in his father's hands, whereas Utsumi was willing to work with Namba's killer the second he had a chance. Furthermore, Gentoku's mental state improved drastically upon becoming a Kamen Rider, whereas Utsumi's...going to end up in a mental institution by the end of the series if he's lucky. And Gentoku is willing to do the right things in order to atone for his previous actions, while Utsumi is starting to do all sorts of wrong things and not feel any regret for his actions [[spoiler:(although it is later revealed that Utsumi was just pretending to join Evolt so that he could get revenge for Namba)]].

* HeelFaceTurn: Episodes 30 through 33 showcase his steady return back to his original kindhearted self, with his heightened Hazard Level thanks to the Sclash Driver having broken the spell the Pandora Box once held him under. And he now joins the heroes as one of the main Riders in the fight against Evolt.

** It turns out the conga line just stalled for a bit. For one, it turns out that raising his Hazard Level has also broken him free of the influence of the Pandora Box. While this does mean that he's good again, it also means that he has to bear the guilt of all of his sins. And he can't stop because Namba made sure to install an ExplosiveLeash onto him in order to force him into doing their bidding, up to forcing him to kidnap his father so that Evolt can have a bargaining tool to get back his Evol Driver. Then, when he finally finds a way to disable his kill chip, he ends up failing to stop Evolt, gets [[CurbStompBattle curb-stomped]] by Kamen Rider Evol's debut, and watches as Taizan ends up TakingTheBullet for him.
* JerkAss: Kidnapping Katsuragi's mother and then forcing her to exchange information for her son's heartfelt will, only for it to be a complete lie was a pretty asshole move on his part. [[spoiler:It takes numerous episodes and getting some sense beat into him repeatedly to finally get better.]]

* ManChild: It turns out, underneath his Pandora's Box affliction, this is his true nature. He's pretty mature and serious most of the time. But that aside? He hates green peppers, can't buy a train ticket by himself, sleeps with a night light [[RummageSaleReject and has the fashion sense]] [[BreadEggsMilkSquick of a sack of mouldy ham]]. Sento even straight-up calls him a baby in the recap of episode 41.

* TheShadowKnows: [[spoiler:When he finally dies fighting Evolt, he falls to his knees untransformed, wondering if he made his father proud even a little bit... but during the scene, his shadow is still the silhouette of Kamen Rider Rogue, showing that he did indeed go down a hero.]]

* UltimateJobSecurity: An absolutely ''infuriating'' example, but even though his father knows he's Faust's leader and a criminal, Gentoku is still Touto's leader due to Hokuto declaring war and Taizan not being fit enough to lead again. That said, [[AvertedTrope the warranty on his job security runs out]] with episode 20, where Taizan comes back and this time wastes no time both disowning Gentoku and running him out of Touto.

* VillainWithGoodPublicity: As far as the public knows, he's the good second in command of the country, who filled in for his father after his stroke and destroyed Faust. [[spoiler:By episode 48, he dies as a hero with good publicity.]]

!! nascita

Prior to the show's events, Soichi was the astronaut who found Pandora Box on Mars 10 years ago and was subsequently possessed by the being known as Evolt. During the unveiling ceremony, Evolt touched the Box, attempting to destroy Earth as he had Mars but ended up initiating the Sky Wall Incident instead. Nine years later, he saved Misora from Faust, at which time he also stole a Pandora's Box panel, the Build Driver, and a number of Fullbottles. Soon after, Soichi encountered an amnesiac Sento in an alleyway and brought him in, encouraging him to use the Driver to become Kamen Rider Build. All of this was part of his schemes as [[Characters/KamenRiderBuildFaust Blood Stalk]], using Sento and Misora to gather all twenty Fullbottles as well as Pandora's Box and both panels for himself. He continues to play a role that alternates in equal parts between mentor and antagonist, raising Sento and Banjo's Hazard Levels in pursuit of his goals: the ultimate vessel and the ultimate Driver. Soon after completing Banjo's growth, Evolt gains the Evol Driver and Evolbottles to transform into Kamen Rider Evol.

For tropes pertaining to when Evolt's not pretending to be Soichi, see his entry under [[Characters/KamenRiderBuildFaust Blood Stalk]].

* AmbiguouslyHuman: At the end of episode 2, he twists a tablet computer into a back scratcher, and continues to demonstrate new abilities as the show progresses. Soichi claims his powers to be a result of having touched Pandora's Box on Mars, although that's not the whole story: his powers come from being possessed by Evolt.

* ConvenientComa: After Evolt leaves his body to possess Ryuga, Soichi is left alive, but unconscious for the time being.
* CordonBleughChef: His coffee is ''horrible''. Even he himself hates it! This takes a darker turn once you realize that [[DemonicPossession Evolt]] is an alien who has no clue how to make coffee and no reason to want to learn. [[spoiler: In the new world where Evolt never existed however, his coffee is ''[[SupremeChef amazing.]]'']]

* DemonicPossession: Ever since he went to Mars, Soichi has been possessed by Evolt, the destroyer of Mars who seeks to do the same to Earth.
* EvilCostumeSwitch: After the events of episode 14, Soichi stops wearing his glasses and starts wearing a lot more black.
* FightingFromTheInside: The reason so many of the Best Matches are so silly is because Soichi fought back against his demonic passenger when Evolt asked him "name 30 things you like", followed by [[KickTheDog "name 30 ways I could kill those things"]]. While at first his answers were things like tanks, gatling guns, rockets, and jets, once Soichi realized why Evolt was asking, he started providing random nonsense answers, and was able to do it for long enough that Evolt gave up and went with the silly bottles. He's also able to briefly wrest control of part of his body from Evolt, but never in a time or place where it particularly helps.

* InASingleBound: Demonstrates this ability at the end of episode 14.

* MoralityPet: Misora is this to him, allegedly. In truth, she's only this to Soichi, not [[DemonicPossession Evolt]], who tries to kill her to kill Vernage.

* OneHourWorkWeek: Soichi is never actually shown working at the cafe, as it's always shown either during off-hours or empty during business hours. Justified as he really ''doesn't'' have any customers, which is lampshaded in Episode 13, but he claims that he keeps the place open out of sentimental value. Further justified as he supports himself with his ''other'' job (with Faust), and it's one that has a good reason to let him hang around the empty café (as Sento's and Misora's handler).

** In Episode 5, he gives a five-minute info dump when Sento confronts him on why he has a piece of Pandora's Box: he was the astronaut that originally found Pandora's Box, and then was suddenly compelled to grab it on Earth, though even he's not sure why. Faust blackmailed him to get Misora's power, until he rescued her and stole a bunch of their tech. He then found Sento and recognized another of Faust's victims, taking him in so he could use the stolen tech to defend them. And he kept all this from Sento because he knew it was a crazy story, so he waited until Sento was actively looking for answers.

** Episode 30 reveals that he's been possessed by Evolt this whole time.

* WalkingSpoiler: As the BigBad of the show and a [[TheChessmaster chessmaster]] par excellence, it's impossible to talk about Soichi, or rather ''Evolt'', in any detail while pretending his early persona is all there is to him.

** In episode 9, after Ryuga takes her into the city, she runs into the clothes shop squeeing in delight, meaning that not all of her attitude as "Mii-tan" is false.

* HiddenDepths: Episode 9 suggest that not all of her attitude as "Mii-tan" is false as she runs into the clothes shop squeeing in delight after Ryuga takes her into the city.

* SymbioticPossession: Misora's bracelet is capable of possessing her, turning her eyes a supernatural shade of green and causing her to display powers that allow her to tear down sections of the Sky Wall as well as easily defeat the Washio brothers and Kamen Rider Rogue. This possessed identity says nothing but the word "Evolt" in its first appearance, [[spoiler:but in its second introduces itself as Vernage, the queen of Mars, and subsequently explains that "Evolt" was the one who destroyed Mars with Pandora's Box]]. Misora doesn't mind, as the entity is protecting her and her friends, and never possesses her except when needed [[spoiler:unlike [[DemonicPossession her father's unwanted stowaway]].]] [[spoiler: As of #43 however, Vernage has been transferred to Ryuga to keep Evolt's DNA in check.]]

** [[spoiler:On a larger scale, her entire situation as seen from episode 1 was orchestrated by Soichi to get her to produce more Fullbottles, under the impression that she was doing good.]]

* ActionGirl: While she can't stand against the superhuman Smash and other antagonists, Sawa's perfectly capable of handling escaping danger on her own without needing to be saved. At times she's even the one to save Sento and Banjou.

* BrainyBrunette: Episode 26 shows she understands schematics and is able to solder delicate circuitry. Sento even comments on this when she helps him work on his latest invention - Full Full [=RabbitTank=] Bottle and Fullbottle Buster.

* BigDamnHeroes: While not the one that did the actual saving, [[spoiler: Sawa is directly responsible for Nabeshima's family being safe and sound.]]

* CarFu: Most of the show's vehicle-related stunts involve Sawa driving a car or truck, which proves effective both at dealing with Guardians and getting Sento and Banjou out of trouble with Hokuto's forces.

* GoodCounterpart: To Utsumi. [[spoiler: Both were indoctrinated by Namba at a very young age, and both seemingly keep working for him, even after being forced into situations that would likely result in them getting killed off normally (Sawa becoming the Octopus Smash, Utsumi having to become Night Rogue to get Gentoku off the hook), and both eventually leave Namba's employment. However, Sawa pulls a full-fledged HeelFaceTurn, for reasons explained below, and is still quite sane. Utsumi, on the other hand, went from working for the BigBadWannabe to the real BigBad...and at best, will likely end up in a mental institute]].
* HeelFaceTurn: After being turned into a Smash, she decides to tell Sento and the others everything. [[spoiler: It stuck too. While Sawa was still feeding Namba some information, she was still aiding Sento along the way. Showcased beautifully in #27-28.]]

* NiceGirl: Always polite and caring to her friends. She remains so [[spoiler: even after her HeelFaceTurn when she finally considers her friends as family.]]
* RedemptionEarnsLife: [[spoiler: If she didn't she would have been just another statistic in Evolt's massive body count like the rest of the Namba faction.]]
* PowerOfFriendship: The whole reason why she is still alive even later into the story. [[spoiler: She was supposed to kill herself once found out like the Namba children are taught, but the time spent in nascita made her yearn for family and life.]]
* SecretKeeper: Due to Sento's and Soichi's mistakes, she becomes this after blackmailing them for info. [[spoiler: Things turn out to be a great deal more complicated.]]

* TykeBomb: [[spoiler: She was raised as a ChildSoldier of Namba Heavy Industries.]] It explains ''a lot'' about her numerous skills detailed above.

* ArchEnemy: Is Evolt's. While she can't currently fight him on even footing, she's the reason he spent millions of years SealedEvilInACan and he's the reason she lost her entire planet and people.

* BigGood: Saves the heroes multiple times, gives them the means to control the Hazard Trigger's powers, and warns them of Evolt and actively opposes him at every turn. In fact, she's the reason the heroes managed to have a fighting chance against him ''at all'': she drained the bottles inside Pandora's Box so Evolt couldn't just open it and destroy Earth.

* GoOutWithASmile: Once she senses that Sento's defeated Evolt for good, she possesses Misora one last time to remark on it and then releases the bracelet's clasp and passes on with a smile on her face.

* PyrrhicVictory: Vernage eventually managed to defeat a fully powered Evolt, but by the time she managed to do so, he had already wiped out the rest of the Martians and destroyed what was left of their civilization. Downplayed, however, as it still trapped him on Mars for millions of years and likely saved a lot of planets from being destroyed by him in the process.
** Evolt and Shinobu tried to invoke this by turning her host, Misora, into the CD Lost Smash, as due to Vernage's power not even Genius Form could save her host from death. Sento bypassed this by using Genius Form's abilities to kick Misora into Ryuga and transfer Vernage to him so she'd survive.
* SpannerInTheWorks: She's ultimately the biggest roadblock to Evolt's plans. If she didn't defeat Evolt all those years ago, he would have just continued his planet destroying spree. And if she didn't follow him to Earth and drain out the Fullbottle essences from the Pandora Box, Evolt would have won the second he touched the Box instead of just the Skywalls forming (not to mention that it means the heroes still have Fullbottles to fight back with after Evolt uses them to create the Evol Trigger).
* SymbioticPossession: Unlike Evolt, she's genuinely benevolent and heroic and Misora is very willing to have her around. She's saved everyone on multiple occasions.

* WorfHadTheFlu: The only reason she's unable to finish off Evolt herself is that her SoulJar isn't able to sustain her indefinitely and her powers are gradually weakening. At her full power she was able to fight a fully powered Evolt to a MutualKill and total the Evol Driver, leaving him stranded on Mars for millions of years.

!! Kamen Riders

----

----

----

!!Tropes as Kamen Rider Grease

----

!! Tropes as Kamen Rider Rogue

** Also don't forget that Faust caused all his problems (including blaming him for murder and turning his sick girlfriend in Smash, causing her death), meanwhile the only problem Sento has is his amnesia.

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

!!!Portrayed by Eiji Akaso (live), Eitoku (suit)

* DeadlyUpgrade: The Sclash Driver draws its overwhelming power from exposing the user to the raw, unfiltered effects of Nebula Gas, which has the same effects on the user's personality as being near the Pandora Box when it was activated. Even the first usage causes Banjou to take on a berserker's fighting style and adds a menacing growl to his voice while wearing the suit, and repeated usage will turn the user into a BloodKnight who can think of nothing but battle. Making matters worse, its mental stresses come with accompanying physical stresses, enough so that just the act of transforming with it for the first time is an agonizing experience and prolonged battle will often see Banjou be overwhelmed by the strain. It takes six episodes of frequent usage for Banjou to finally acquire an immunity to the physical stresses of the Driver.

* WhenAllYouHaveIsAHammer: Since Sento hoards most of their [=FullBottles=], Banjou typically only has access to the Dragon and Lock combo components, if he even has those. Without his partner's diversity of options, Banjou has just one tactic in battle: to punch his problems harder and force his Hazard Level to rise until he can overwhelm his opponent with brute force. That said, he relies on this tactic for a good reason: ''it always works''. No matter how desperate the situation, Banjou can accomplish seemingly impossible feats through sheer grit and willpower.

!!!Portrayed by Kensei Mikami (live), Jun Watanabe (suit)

!!!Portrayed by Yasuyuki Maekawa, Tetsuo Kanao (voice)

!!!Portrayed by Kaho Takada (live), [[spoiler:Creator/SoraAmamiya (voice only, as Vernage)]]

!!!Portrayed by Yukari Taki

!! Others

[[folder: Vernage (SPOILERS)]]

!!!Voiced by Creator/SoraAmamiya

[[/folder]]

*** After receiving the Dragon Fullbottle and discovering in the middle of another fight that it gives him a PowerFist when shaken, he declares it'll make dealing with his opponents easy, [[RealityEnsues until a moment later he realizes he now has a half-dozen guns pointed at him]].

* InstantAwesomeJustAddDragons: He's the dragon-themed Rider of this season.

** Sento's not above this when he's in full control either - upon gaining a FlashStep in Genius Form, [[GameBreaker he starts spamming it gratuitously.]]

* DarkestHour: [[spoiler:Sento's occurs not during the series, but in ''[[Film/KamenRiderBuildBeTheOne Be The One''. He's been completely isolated by the Blood Race, who brainwashed all of Japan (including Banjou, Misora, and Sawa) into hating Build, and captured Kazumi and Gentoku since they can't be brainwashed. After being defeated by Banjou, the BigBad 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: [[TrueCompanions his bond with Banjou]], and his father's belief in [[ArcWords Love and Peace]], which gives him the resolve to keep fighting and save the world.]]

* WhiteHairBlackHeart: [[spoiler: Evolt manages to possess Sento in #36, turning his entie head of hair white in the process.]]

!!Soichi Isurugi / Blood Stalk / Kamen Rider Evol

!!Misora Isurugi / CD Lost Smash

* ClingyMacGuffin: The golden bracelet that's been stuck to Misora's left wrist ever since the Sky Wall went up is the source of her mysterious abilities. It's later found to contain [[spoiler: the soul of Vernage, The queen of Mars, who]] shows Misora the destruction of the Martian civilization whenever [[spoiler: her]] powers are used.

* ShipTease: Despite their bickering she is always looking out for Sento. Be it worrying about him dying or cheering him up when he’s down she will always be there for him. It is also hinted she may have feelings for him.

* SymbioticPossession: Misora's bracelet is capable of possessing her, turning her eyes a supernatural shade of green and causing her to display powers that allow her to tear down sections of the Sky Wall as well as easily defeat the Washio brothers and Kamen Rider Rogue. This possessed identity says nothing but the word "Evolt" in its first appearance, [[spoiler: but in its second introduces itself as Vernage, the queen of Mars, and subsequently explains that "Evolt" was the one who destroyed Mars with Pandora's Box]]. Misora doesn't mind, as the entity is protecting her and her friends, and never possesses her except when needed [[spoiler:unlike [[DemonicPossession her father's unwanted stowaway]].]] [[spoiler: As of #43 however, Vernage has been transferred to Ryuga to keep Evolt's DNA in check.]]

** Also best demonstrated in ''NEW WORLD: Grease'', where she starts out with getting angry at Kazumi for thinking that what they were doing was a "date" when in reality she wanted to buy a birthday gift for Soichi, causing Kazumi to sail away on the boat with the Crows. However, upon her awareness of Kazumi's determination to save her and help stop Downfall, at the end, she ultimately reciprocates his feelings and agrees to date him ''for real this time'', to his joy.

* SingleTargetSexuality: To Misora, and tries to get to get her to recuperate said feelings [[HopelessSuitor to no avail]]. [[spoiler:At least until ''[[Film/KamenRiderBuildNewWorldKamenRiderGrease New World:Grease]]'']].

* SingleTargetSexuality: To Misora, and tries to get to get her to recuperate said feelings [[HopelessSuitor to no avail]]. [[spoiler:At least until ''[[Film/KamenRiderBuildNewWorldGrease New World:Grease]]'']].

* SingleTargetSexuality: To Misora, and tries to get to get her to recuperate said feelings [[HopelessSuitor to no avail]]. [[spoiler:At least until [[Film/KamenRiderBuidNewWorldGrease New World:Grease]]]].

* SingleTargetSexuality: To Misora, and tries to get to get her to recuperate said feelings [[HopelessSuitor to no avail. [[spoiler:At least until [[Film/KamenRiderBuidNewWorldGrease New World:Grease]]]].

* HybridPower: [[spoiler: Katsuragi, while studying Ryuga, determined that his unique genetics meant that his ever escalating Hazard Level might one day allow him to surpass Evolt in power. This eventually came through when he used the Muscle Galaxy Fullbottle to transfom into Cross-Z Evol, whose potential exceeds both Evolt and Kilbas]].

* SingleTargetSexuality: To Misora, and spends the series.

* AnIcePerson: [[spoiler: As Grease Blizzard]].

* DarkestHour: [[spoiler: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 Banjou, Misora, and Sawa) into hating Build, and captured Kazumi and Gentoku since they can't be brainwashed. After being defeated by Banjou, the BigBad 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: [[TrueCompanions his bond with Banjou]], and his father's belief in [[ArcWords Love and Peace]], which gives him the resolve to keep fighting and save the world.]]

* 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 PsychopathicManchild turning up at the rare occasion he jokingly threatens someone with his newest weapon after building it.

* AllYourPowersCombined: [[spoiler: Genius Form lets him access the power of all 60 Fullbottles at will. This is first seen in episode 42 where Build is able to use the Diamond Fullbottle's shielding powers to defend against Evol's Steam Attack.]]

* AnIcePerson: Using the Blizzard Knuckle allows Cross-Z to use special ice powers, although it's soon revealed that the Knuckle's not really meant for him: rather, it's meant as an upgrade for [[Characters/KamenRiderBuildHokuto Grease]].

* FusionDance: [[spoiler:[=Cross-ZBuild=] is him and Build merged into one.]]
** [[spoiler: Later on, [=Cross-ZEvol=] operates under the same principle.]]

* StoryBreakerPower: Cross-Evol, which incorporates a fused Evolt, is as strong the ridiculously powerful Kilbus- who can easily handle Cross-Z Magma (stronger than initial Evol Black Hole) and Evol Cobra in a two on one fight.

* {{Adorkable}}: After learning that Misora is Mii-tan, every interaction that Kazumi has with her is full of this.

* {{Adorkable}}: Misora has her moments, such as in episode 6 where Sawa asks her if she has a boyfriend and if she prefers Sento or Ryuga, which causes her to get very embarrassed and flustered, even causing her to pour too much hot sauce into her pizza.

[[quoteright:210:https://static.tvtropes.org/pmwiki/pub/images/ryuga.png]]

[[quoteright:210:https://static.tvtropes.org/pmwiki/pub/images/kazumi_sawatari.jpg]]

[[quoteright:220:https://static.tvtropes.org/pmwiki/pub/images/gentoku.png]]
[[quoteright:220:https://static.tvtropes.org/pmwiki/pub/images/rogue_man.png]]
[[caption-width-right:220:Gentoku during his time at Seito]]
[[quoteright:220:https://static.tvtropes.org/pmwiki/pub/images/casual_gentoku.jpg]]
[[caption-width-right:220:Gentoku after his HeelFaceTurn]]

[[quoteright:210:https://static.tvtropes.org/pmwiki/pub/images/souichi_profile.png]]

[[quoteright:188:https://static.tvtropes.org/pmwiki/pub/images/saki_8.png]]