History Sandbox / KamenRiderDenOKamenRiderZeronos

* CorruptedCharacterCopy: This Yuto acts as one for Reiji Kurosaki, a member of the [[TimePolice G-Men]] who transforms into G Den-O with the artificial Imagin Eve who is sent to apprehend anyone trying to tamper with the time stream. The Yuto of the BadFuture was chosen to become Kamen Rider Zein to purge all Kamen Rider villains to make way for Zein's utopian ideals. Both of their "partners" react differently to their hosts' showing hesitation, Eve strips Kurosaki of his Rider power and uses it for himself to wipe out all humanity, whereas Zein immediately possesses Yuto once Ark is taken out of the picture and proceeds to use a DeadlyGame to send humanity into their own self-destruction.

[[center: [- [[Characters/KamenRiderDenO Main Character Index]] | [[Characters/KamenRiderDenOProtagonists Protagonists]] ('''Yuta Sakurai and Deneb''') | [[Characters/KamenRiderDenOImagin Imagin]] | [[Characters/KamenRiderDenOMovieExclusiveCharacters Movie-Exclusive Characters]]]] -]

* CastingGag: Yuichi Nakamura once again portrays a FallenHero whose turn to villainy was a result of losing their significant other. Just like [[Film/UltramanTriggerNewGenerationTigaTheMovieEpisodeZ Zabil]], the alternate Yuto Sakurai abuses the power of another hero to his personal gain. The only difference is that while Zabil takes on the form of Evil Trigger, who is a MirrorMatch of the being whose powers he stole from, Yuto as Zein transforms through the belt that incorporates technology from [[Series/KamenRiderZeroOne Zero-One]], gimmicks from [[Series/KamenRiderDecade Decade]] created by a character from Revice. Said Rider resembles a villain from [[Series/KamenRiderKuuga Kuuga]][[labelnote:In this case]]N-Daguva-Zeba, the show's BigBad.[[/labelnote]]

* AlternateSelf: The Yuto Sakurai who transforms into Kamen Rider Zein is an entirely separate character from the one we are all familiar with. He actually comes from a BadFuture where his fiancée met a seemingly tragic fate, keyword being "seemingly" as the circumstances regarding the Airi Nogami of that Yuto's timeline isn't elaborated upon.

* BadFuture: He comes from a certain alternate future where he DidNotGetTheGirl and suffered to tragic circumstances.
* BecameTheirOwnAntithesis: In ''Series/KamenRiderZiO'', part of Yuto's motivation to stop Sougo was because he feared that him becoming Ohma Zi-O would doom the timeline, but was convinced to stop after seeing Sougo's conviction. In ''Series/KamenRiderOutsiders'', this version of Yuto Sakurai becomes Kamen Rider Zein, who not only brutally punishes villains under twisted justice, but also works under an AI that plans to create a WorldOfSilence, effectively dooming his timeline if it succeeds.

* FallenHero: He used to be Kamen Rider Zeronos, and considering that he's from a BadFuture where he loses Airi, he willingly allowed himself to become Zein's enforcer to exterminate all villainous Riders.
* HeWhoFightsMonsters: Yuto spends his appearance in ''Series/KamenRiderZiO'' for two episodes trying to kill Sougo, fearing his potential to become Ohma Zi-O and doom the timeline, but eventually changed his mind after witnessing Sougo's conviction. Come to the third episode of ''Outsiders'', this version of Yuto displays himself as the enforcer of Zein's will through the titular Rider form, as not only he can use a plethora of past Rider powers like Decade and Zi-O, but actively plays along with the namesake AI's authoritarian goals, hence seeing him slowly [[BecameTheirOwnAntithesis walking the same path]] as Sougo as Ohma Zi-O.

* OhCrap: Yuto looks on in horror upon seeing Ark-Zero getting obliterated along with ''Horobi''.

* ShadowArchetype: The main universe Yuto spends his appearance in ''Series/KamenRiderZiO'' for two episodes trying to kill Sougo, fearing his potential to become Ohma Zi-O and doom the timeline, but eventually changed his mind after witnessing Sougo's conviction. Come to the third episode of ''Outsiders'', this Yuto displays himself as the enforcer of Zein's will through the titular Rider form, as not only he can use a plethora of past Rider powers like Decade and Zi-O, but actively plays along with the namesake AI's authoritarian goals, hence seeing him slowly [[BecameTheirOwnAntithesis walking the same path]] as Sougo as Ohma Zi-O.

* WalkingSpoiler: He himself becomes this even more as the user of the Zein Driver, given that no details on who the human user of Kamen Rider Zein is, and it's impossible to talk about the circumstances of him becoming Kamen Rider Zein without revealing what happened to his version of Airi in that timeline.

* BewareTheSuperman: Even more so than the likes of [[Series/KamenRiderDecade Decade]] and [[Series/KamenRiderZiO Ohma Zi-O]], given that he can {{Power Copy|ing}} the {{Finishing Move}}s of all Kamen Riders and he serves as Zein's enforcer to carry out the [[FinalSolution complete extermination of every single Kamen Rider villain]] to ensure its {{totalitarian|Utilitarian}} {{utopia|JustifiesTheMeans}} becomes reality. The first thing Yuto does as Kamen Rider Zein is beating Banno within an inch of his life through [[Series/KamenRiderExAid Muteki Gamer]]'s finisher, reducing him into a whimpering wreck [[MookHorrorShow hopelessly trying to escape with his life]] before turning him into a human pincushion with Xross Saber's Haou Xross Sei Retsuzan.
* CorruptedCharacterCopy:
** Of Series/KamenRiderDecade. Interestingly, Kamen Rider Zein acts more like Decade Violent Emotion, further emphasizing his BewareTheSuperman tendencies. Tsukasa Kadoya is an interdimensional traveler who transforms into Decade, and with the Rider Cards in his disposal, can transform into his predecessors and successors. Yuto Sakurai is a non-Singularity Point who time travels and previously transforms into Kamen Rider Zeronos. The Zein Cards are a knockoff of Decade's Cards, with the obvious difference being Zein's logo in the place of a Legend Rider's logo under the Rider's visage and at the back of the cards. Tsukasa takes his role as the "Destroyer of Worlds" if the Rider multiverse is under imbalance, while Zein, the AI, seeks to merge all the Rider universes into one in order to expunge all human malice.
** Crossing with AlternateCompanyEquivalent, Kamen Rider Zein could be seen as a corrupted version of [[Franchise/SuperSentai AkaRed]]. [=AkaRed=] is the embodiment of all Red Sentai Rangers who represents their sense of justice and determination in their fight against evil and he can even transform into Red Rangers of previous and current seasons whenever he appears in a ''Super Sentai'' anniversary crossover. Zein, both the AI and Rider, is presented as a DarkMessiah that seeks to bring salvation to humanity and expunge evil. Zein also represents the [[BewareTheSuperman worst traits]] of all the heroic main Riders and a cautionary tale that even in ''Kamen Rider'', absolute power corrupts absolutely. Zein can {{Power Copy|ing}} the abilities of previous and current Riders through the Zein Cards.
* EvilKnockoff: The Zein Cards are artificial copies of Decade's Rider Cards, denoted by Zein's symbol being marked on the back instead of the one for whoever is on the card.
* EvilerThanThou: To show off how dangerous he is, he manages to fully brutalize [[Series/KamenRiderDrive Tenjuro Banno/Bronze Drive]], who himself once applied this trope onto the Roidmudes, by completely curb-stomping him.

* HoldingBackThePhlebotinum: The Zein Cards can only be used once, and is shredded after doing so, as while there's no known cost for him to use the Zein Driver, the Rider Cards Foundation X has given him [[ItOnlyWorksOnce get shredded after their initial use]] and therefore require him to ration their various {{Story Breaker Power}}s carefully.

* ItOnlyWorksOnce: Any card inserted into the Zein Driver's middle scanner will be shredded after Yuto is done using it, destroying the copy of its powers contained within.

* KnightOfCerebus: ''Outsiders'' is, if anything, [[DarkerAndEdgier never lighthearted from the start]] compared to other previous TTFC specials and miniseries as this is about a supposedly BenevolentAI that wants a world without malice. And the returning villains featured in the series ranging from redeemed {{Anti Villain}}s, [[TheSociopath bloodthirsty psychopaths]], [[AGodAmI cartoonish god wannabes]], to a NebulousEvilOrganization. Kamen Rider Zein takes BewareTheSuperman to another whole new level since his introduction, showing no mercy [[CurbStompBattle when he beats Banno within an inch of his life before turning him into a human pincushion]]. Giving the villains enough good reason to oppose Zein's utopian ambitions.

* TransformationTrinket: The Zein Driver, which is designed by [[Series/KamenRiderRevice George Karizaki]] to utilize the powers of every heroic Rider, and it appears to comprise of an unnamed [[Series/KamenRiderZeroOne Progrisekey]] alongside a scanner that allows him to use the Rider Card's power within only once.
* VillainKiller: As Kamen Rider Zein, he carries out the eponymous' artificial intelligence's task of eliminating the Kamen Rider Outsiders team with extreme prejudice. [[Series/KamenRiderDrive Tenjuro Banno]] is the first to fall victim to Zein's dominance, and the way the MadScientist is beaten within an inch of his life is [[BewareTheSuperman anything but heroic]].

* FinishingMove: '''Justice Order''': Zein scans (and shreds) a Final [=KamenRide=] card, allowing him to copy one of the corresponding form's finishers once.
** '''[[Series/KamenRiderExAid Ex-Aid Hyper Muteki]]''': Zein performs the Hyper Critical Sparking, augmenting it with his SuperSpeed to strike the target from all directions before pummeling them into the sky.
** '''[[Series/KamenRiderSaber Xross Saber]]''': Zein draws the Haouken Xross Saber and performs an abridged version of the Haou Xross Sei Retsuzan, skewering the opponent with all 12 Seikens.
** '''[[Series/KamenRiderBlade Blade King Form]]''': Zein performs Four of a Kind/Four Cards by summoning the King Rouzer along with four Category King cards: Evolution Caucasus ♠K, Evolution Paradoxa ♥K, Evolution Giraffa ♦K, Evolution Tarantula ♣K, and a Category Ace card: Change Beetle ♠A. Zein loads the cards into the King Rouzer and charge towards the card projections to deliver a downward slash.

Airi's fiance and Ryotaro's future brother-in-law, Sakurai was a gentle, kind-hearted man with a passion for astronomy he shared with Airi. The two were very much in love, and Sakurai treated Ryotaro like the little brother he never had; thus, Ryotaro's surprise when Sakurai disappeared just before the wedding is understandable, as is his confusion at the fact that nobody seems to remember his existence. Several times in the early part of the series, a cloaked man appears watching Den-O's battles in the past and checking a pocketwatch; by accident, Ryotaro bumps into the man and recognizes him as Sakurai. He attempts to track down the man, only to be warned off by Yuto.

* CrosscastRole: Ruka Sawaki is a girl.

* ShooOutTheClowns: The moment where he becomes conspicuously absent in ''Series/KamenRiderOutsiders'' is when Yuto decides to become the user of the Zein Driver and become Kamen Rider Zein, a KnightTemplar who is [[BewareTheSuperman dedicated to eradicating evil in the most brutal way possible]].

* WhatHappenedToTheMouse: He's nowhere to be seen during ''Series/KamenRiderOutsiders'', which is strange given that it's mentioned that every heroic rider gave their power to Zein.

* AlternateSelf: This Yuto Sakurai comes from an alternate BadFuture where he didn't fight for Airi's sake and something tragic befell her.

* FaceHeelTurn: In ''Series/KamenRiderOutsiders'', he has sided with Zein and became the user of Kamen Rider Zein, and unlike others who are ambiguously loyal to him, it's clear that he has consented to being loyal to it.

* HeWhoFightsMonsters: Yuto spends his appearance in ''Series/KamenRiderZiO'' for two episodes trying to kill Sougo, fearing his potential to become Ohma Zi-O and doom the timeline, but eventually changed his mind after witnessing Sougo's conviction. Come to the third episode of ''Outsiders'', This version of Yuto displays himself as the enforcer of Zein's will through the titular Rider form, as not only he can use a plethora of past Rider powers like Decade and Zi-O, but actively plays along with the namesake AI's authoritarian goals, hence seeing him slowly [[BecameTheirOwnAntithesis walking the same path]] as Sougo as Ohma Zi-O.

* RunningGag: Sixteen years later, he gets a massive power boost by becoming Zein's host. Yet even after switching to [[Series/KamenRiderZeroOne Progrisekeys]] and [[Series/KamenRiderDecade Rider Cards]], he's ''still'' unable to make full use of his powers and fulfill his purpose without slowly burning away ''another'' set of plot-significant cards.

* WellIntentionedExtremist: This version of Yuto Sakurai, along with Zein, seeks to eliminate all villains from the ''Kamen Rider'' timeline. However, the fact that Zein considers ''all'' Kamen Riders evil as well regardless of how evil they are or not means that he is at with odds with those who oppose Zein.

* FinishingMove:
** '''Justice Order''': Zein scans (and shreds) a Final [=KamenRide=] card, allowing him to copy one of the corresponding form's finishers once.
*** '''[[Series/KamenRiderExAid Ex-Aid Muteki Gamer]]''': Zein performs the Hyper Critical Sparking, augmenting it with his SuperSpeed to strike the target from all directions before pummeling them into the sky.
*** '''[[Series/KamenRiderSaber Xross Saber]]''': Zein draws the Haouken Xross Saber performs an abridged version of the Haou Xross Sei Retsuzan, skewering the opponent with all 12 Seikens.
*** '''[[Series/KamenRiderBlade Blade King Form]]''': Zein performs Four of a Kind/Four Cards by summoning the King Rouzer along with four following cards: Evolution Caucasus ♠K, Evolution Paradoxa ♥K, Evolution Giraffa ♦K, Evolution Tarantula ♣K, and Change Beetle ♠A. Zein loads the cards into the King Rouzer and charge towards the card projections to deliver a downward slash.

* WellIntendedExtremist: This version of Yuto Sakurai, along with Zein, seeks to eliminate all villains from the ''Kamen Rider'' timeline. However, the fact that Zein considers ''all'' Kamen Riders evil as well regardless of how evil they are or not means that he is at with odds with those who oppose Zein.

[[Series/KamenRiderOutsiders Sixteen years after the end of the Imagin conflict]], the AI Zein enlisted him to assume the mantle of Kamen Rider Zein, an omniscient and omnipotent dimensional warrior powered by an ArtificialIntelligence of the same name obsessed with eliminating evil [[KnightTemplar at any cost]].

* AmbiguouslyEvil: As shown in ''Series/KamenRiderOutsiders'', he is chosen be the user of Kamen Rider Zein, and according to [[Series/KamenRiderBlade Sakuya Tachibana]], he along Yuto consented to offer up their powers to him. However, Zein itself is AmbiguouslyEvil, and while its intentions are well-meaning, the fact that it considers all Kamen Riders to be evil are questionable, and it isn't helped that most of the information against it came from [[Series/KamenRiderZeroOne Gai Amatsu and the Ark]], and the fact that [[Series/KamenRiderDouble Foundation X]] helped in the design of Zein only muddies the waters.
* AscendedMeme: For his 33rd birthday, Yuichi Nakamura [[https://twitter.com/NvKknpbmkIbDg6m/status/1313856693285969920 made a tweet about himself]] wearing ''twenty-three'' rider belts on him, with comments comparing it to Series/KamenRiderDecade Complete Form and [[Series/KamenRiderZiO Ohma Zi-O]]. In ''Series/KamenRiderOutsiders'', he becomes Kamen Rider Zein, which essentially combines the powers of all Riders bestowed on him like Decade and Ohma Zi-O.

* BecameTheirOwnAntithesis: In ''Series/KamenRiderZiO'', part of his motivation to stop Sougo was because he feared that him becoming Ohma Zi-O would doom the timeline, but was convinced to stop after seeing Sougo's conviction. In ''Series/KamenRiderOutsiders'', he becomes Kamen Rider Zein, who not only brutally punishes villains under twisted justice, but also works under an AI that plans to create a WorldOfSilence, effectively dooming his timeline if it succeeds.

* FaceHeelTurn: In ''Series/KamenRiderOutsiders'', he has sided with Zein and became the user of Kamen Rider Zein, and unlike others who are ambiguously loyal to him, it's clear that he has consented to being loyal to it.

* HeWhoFightsMonsters: His spends his appearance in ''Series/KamenRiderZiO'' for two episodes trying to kill Sougo, fearing his potential to become Ohma Zi-O and doom the timeline, but eventually changed his mind after witnessing Sougo's conviction. Come to the third episode of ''Outsiders'', Yuto displays himself as the enforcer of Zein's will through the titular Rider form, as not only he can use a plethora of past Rider powers like Decade and Zi-O, but actively plays along with the namesake AI's authoritarian goals, hence seeing him slowly [[BecameTheirOwnAntithesis walking the same path]] as Sougo as Ohma Zi-O.

* HoldingBackThePhlebotinum: With good reason. And, apparently, Sakurai himself has a good reason for giving power with such a drawback in the first place. Erasing [[HeroicSacrifice his (Sakurai's) own existence]] allows Yuto to [[ScrewDestiny write his]] ''[[ScrewDestiny own]]'' [[ScrewDestiny history]] (in another timeline, anyway). Once he becomes Zein, this still sticks somewhat, as while there's no known cost for him to use the Zein Driver, the Rider Cards Foundation X has given him [[ItOnlyWorksOnce get shredded after their initial use]] and therefore require him to ration their various {{Story Breaker Power}}s carefully.

* {{Irony}}: In ''Series/KamenRiderZiO'', he traveled to 2018 to prevent Sougo from becoming Ohma Zi-O, a tyrant who rules over a BadFuture by drawing the powers of the riders before 2068. In ''Series/KamenRiderOutsiders'', he assists with Zein to eradicate all the evil by defeating all Kamen Riders, both good and evil, and to impose his authoritian rule over humanity, essentially becoming Ohma Zi-O in name, and it's even implied that Sougo consented to giving his powers to Zein as well.

* JerkWithAHeartOfGold: Yes, he does distance himself from people in a rude way, but he does have legit reasons for doing so, given that he is doing everything to protect his niece Hana. As Zein, he still qualifies, [[KnightTemplar albeit for very different reasons]].

* WalkingSpoiler: The truth behind the source of his powers are meant to be a late-series surprise. He himself becomes this even more as the user of the Zein Driver, given that no details on who the human user of Kamen Rider Zein is.
* WellIntentionedExtremist:
** In ''Series/KamenRiderZiO'', he spends most of episode 39 trying to kill Sougo because he believes Sougo is destined to be corrupted by his power and create a horrible future.
** In ''Series/KamenRiderOutsiders'', he, along with Zein, seeks to eliminate all villains from the ''Kamen Rider'' timeline. However, the fact that Zein considers ''all'' Kamen Riders evil as well regardless of how evil they are or not means that he is at with odds with those who oppose Zein.

* YankTheDogsChain: Sixteen years later, he gets a massive power boost by becoming Zein's host. Yet even after switching to [[Series/KamenRiderZeroOne Progrisekeys]] and [[Series/KamenRiderDecade Rider Cards]], he's ''still'' unable to make full use of his powers and fulfill his purpose without slowly burning away ''another'' set of plot-significant cards.

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* BewareTheSuperman: The first thing he does as Kamen Rider Zein is dishing out a CurbStompBattle on [[Series/KamenRiderDrive Banno]], enough to leave him scared shitless before skewering him to death with [[Series/KamenRiderSaber Xross Saber's]] FinishingMove. And Banno's destruction is merely the extent of Zein (the AI) demonstrating its [[KnightTemplar twisted sense of justice]] upon humanity.

* {{Foil}}: To Series/KamenRiderDecade Violent Emotion. Both their users' roles are to defeat all Kamen Riders, and they even use Rider Cards as part of their powers. However, there are major differences: while Violent Emotion was intended to further Dai-Shocker's plans of conquering the entire world, Tsukasa Kadoya merely accepted the role as part of a gambit to guide Natsumi into taking him down so that all the worlds destroyed by him are restored, while Zein seeks to defeat all riders to create peace throughout the world, and Yuto accepts it willingly.
* {{Homage}}: Kamen Rider Zein's design more or less bears a striking resemblance to [[spoiler:[[Series/KamenRiderKuuga N-Daguva-Zeba]]. Matters helped when [[Series/KamenRiderRevice the man who developed the Zein Driver]] happens to transform into a Rider based on Kuuga Ultimate Form and is a die-hard Kamen Rider fanboy]].

* LightIsNotGood: The bright colorings of Kamen Rider Zein belie the KnightTemplar beneath it that wishes to erase all ''Kamen Rider'' villains even if it disturbs the BalanceBetweenGoodAndEvil.

* VirtuousCharacterCopy: As Kamen Rider Zein, he is this to [[Series/KamenRiderZiO Ohma Zi-O]]. The latter's present self draws power from Ridewatches to tap into the powers of his predecessors who seeks to become a benign ruler. The Sougo of 2068 is a ruthless tyrant who has brought humanity down to its knees with the powers of all Kamen Riders in his disposal. Kamen Rider Zein draws power from artificially-made [[Series/KamenRiderDecade Rider Cards]] that allows the user to invoke the ability of every Showa-Reiwa Riders, albeit for [[ItOnlyWorksOnce one-time use]]. Yuto as Zein's host is tasked to [[BewareTheSuperman eradicate all evil Kamen Riders]] in order for Zein to impose its authoritarian rule upon humanity. Ironically, Yuto's appearance in Zi-O's ''Den-O'' tribute episodes has him stop Sougo from becoming Ohma Zi-O; but when he resurfaces and aligned himself with Zein, he starts to act more and more like Ohma Zi-O.

[[Series/KamenRiderOutsiders Sixteen years after the end of the Imagin conflict]], Foundation X chooses him to become Kamen Rider Zein, an omniscent and omnipotent dimensional warrior powered by an ArtificialIntelligence of the same name obsessed with eliminating evil [[KnightTemplar at any cost]].

* BroughtToYouByTheLetterS: (A)ltair and (V)ega, which is visible on both their corresponding Zeronos cards, the [=ZeroLiner's=] cars, and their {{Finishing Move}}s.

* UnPerson: The cost of using his powers, due to not being a Singularity Point. The more cards he uses, the more his and Sakurai's existance in people's memories are erased, subsequently erasing them from reality itself. The first signs of this was the fact that Sakurai had disappeared just before his wedding with Airi, with no one (including the latter, except for Ryotaro), remembering him since.

* BewareTheSuperman: The first thing he does as Kamen Rider Zein is dishing out a CurbStompBattle on [[Series/KamenRiderDrive Banno]], enough to leave him scared shitless before skewering him to death with [[Series/KamenRiderSaber Xross Saber's]] FinishingMove. And Banno's destruction only serves as Zein (the AI) demonstrating its [[KnightTemplar twisted sense of justice]] upon humanity.

* {{Foil}}: To Series/KamenRiderDecade Violent Emotion. Both their users' roles are to defeat all Kamen Riders. However, there are major differences: while Violent Emotion was intended to further Dai-Shocker's plans of conquering the entire world, Tsukasa Kadoya merely accepted the role as part of a gambit to guide Natsumi into taking him down so that all the worlds destroyed by him are restored, while Zein seeks to defeat all riders to create peace throughout the world, and Yuto accepts it willingly.