This play assumes that the audience already watched Kamen Rider Gaim, since endgame events and plotpoints are important to the story. Therefore, spoilers for Gaim and it's related spin-offs will be unmarked. You Have Been Warned!
Kamen Rider Zangetsu -Gaim Gaiden- is a 2019 stage play Spin-Off of the Japanese television series Kamen Rider Gaim, later released on DVD. Actor Yuki Kubota reprises his role as Takatora Kureshima/Armored Rider Zangetsu in this story co-authored by nitro+'s Jin Haganeya and Toei Company’s Nobuhiro Mouri, both of whom were secondary writers on the Gaim TV series (with Haganeya serving as assistant to the show's head writer, Gen Urobuchi).
Several years after fighting off the Helheim Forest invasion, Takatora Kureshima is traveling the world, cleaning up the messes left behind by the now-dissolved Yggdrasil Corporation. While investigating their former test site in the Torkia Republic, he's shot by a mysterious assailant and falls into the Underground City, where young men are given Sengoku Drivers and Lockseeds and forced to fight to the death for the amusement of the ruling elites. Stricken with amnesia, Takatora must slowly recover his memories and unravel the dark secrets behind the republic — as well as the identity of the Revenge-obsessed man who attacked him.
Kamen Rider Zangetsu gives us these tropes:
- Apocalypse How: A Class 0 happened in the backstory, where the Scalar System in the Trokia Republic was activated and turned much of the country into a smoldering crater, setting up the events of the play.
- The Atoner: Takatora openly says that he's trying to make up for his sins as the head of Yggdrasil by investigating their old research sites an making sure it's all been shut down. At the end of the play he says he's still got a lot of work to do.
- Big Bad: Masahito Shizumiya, Takatora's former friend, who briefly hijacks the role of Armored Rider Zangetsu and has become an Overlord Inves.
- But Now I Must Go: The story ends with Takatora leaving the Trokia Republic in the capable hands of his new allies and setting off to investigate Yggdrasil sites all around the world.
- Cast of Expies: An internal example occurs here, since every named character is an obvious stand-in for a character from Gaim itself. This gets acknowledged by Takatora when he remarks that Aim reminds him of Kouta Kazuraba, and is actively exploited by Kagemasa (Mitsuzane/Micchy's Expy), who briefly convinces the amnesiac Takatora that he is Mitsuzane.
- Character Development: When Takatora first meets him, Aim is downright glib about the fact that he's killed people before, saying that that's just how it is in Trokia and not really giving it any further thought. As the story progresses, he begins understanding the value of human life and ends up developing the same "I'll save everyone!" attitude as Kouta.
- Combat Breakdown: During the final battle both Takatora and Masahito lose their transformations and end up facing off against each other in their civvies (but still wielding their super-powered weapons).
- Composite Character: Foras is an obvious Expy to Hideyasu Jonouchi/Gridon, being a Smug Snake who ends up as the comedic minion of Bravo...but unfortunately for him he also turns out to be an Expy of Ryoji Hase/Kurokage, transforming into an Inves and having to be put down by Gaim.
- Darker and Edgier: You might not think it's possible to make a Gen Urobuchi story even darker, but Zangetsu replaces the street dancing and Mons battles of Gaim with a straight-up Hunger Games-style death battlenote , where practically every named character (even the Kouta Expy) has committed at least one murder by the time the story even begins and they just accept killing as a fact of life. There's also a lot of battles between non-transformed humans wielding knives, guns, and pipes, but it manages to avoid being Bloodier and Gorier because the production doesn't use a single drop of stage blood.
- Dark Is Not Evil: Yukimura Belial Grunstein might have a name that's associated with Satan, but he's essentially just the play's Expy for Pierre Oren Alfonso/Armored Rider Bravo: a mercenary who turns out to have a Hidden Heart of Gold.
- A Day in the Limelight: As the title implies, this is Takatora's stage now. The only other Gaim cast member to return (as such) is Hōchū Ōtsuka, the narrator.
- Demonic Possession: Not "demonic" at all, but late in the story Kouta uses his "Man of the Beginning" powers to briefly borrow Aim's body, giving Takatora some words of encouragement and creating a green version of the Kachidoki Lockseed for him to use.
- Drama-Preserving Handicap: Takatora's skill and experience as Armored Rider Zangetsu could easily resolve the entire situation in about five minutes...which is why he loses both his memory and the Melon Lockseed about three minutes into the playnote .
- The Dreaded: Much like Takatora himself in Gaim, when the new Zangetsu enters the battle and starts curb-stomping all the other Riders at the same time, they rightly learn to fear him.
- Dying as Yourself: As he's defeated, Masahito has a final moment of clarity where he realizes his misdeeds, apologizes to Takatora, and asks his friend to remember him before he spreads his arms and leaves himself open for the deathblow.
- Easy Amnesia: Takatora loses his memories at the start of the play, after getting shot and falling into the Underground City. Over the course of the story he slowly regains bits and pieces as the events unfolding around him remind him of Zawame City, before finally making a full recovery around 2/3 of the way through.
- Evil Counterpart: Masahito is obviously meant to be Takatora without the nobility and buried idealism, instead being selfish and power-hungry.
- Evilutionary Biologist: Kagiomi Shizumiya gave malfunctioning prototype Sengoku Drivers to the people of the Trokia Republic, knowing that they would slowly transform the wearers into Inves, with the intent of achieving a level of existence beyond either humans or Inves. His son Masahito, who already achieved this by becoming an Overlord, just wants to Take Over the World.
- Extreme Speculative Stratification: The Trokia Republic is divided 20/80 between the rich elites who live on the surface and the poor "have-nots" who are forced to live in the Underground City and engage in super-powered deathmatches for the amusement of their "betters".
- Fake Shemp: Kouta returns by temporarily possessing the body of Aim; presumably, Keigo Hagiya was cast in the role because his voice is fairly similar to Gaku Sano's, which adds to the illusion.
- Flawed Prototype: The Sengoku Drivers used in the story are incomplete prototypes, and overuse causes one to eventually transform into an Inves. The Shizumiya family, who were part of Yggdrasil, were fully aware of this and used them to experiment on the unwitting populace.
- Forced Transformation: The Sengoku Drivers used by Trokia's Riders are incomplete prototypes, meaning the power from the Lockseed "leaks" into the user and slowly transforms them into an Inves. This happens to both Foras and Team Orange Ride's previous Leader.
- A God Am I: The Big Bad Overlord Masahito believes himself to be above humanity and thus the rightful ruler of the planet.
- History Repeats:
- According to the Big Bad, the tragedy of the Trokia Republic is that they keep repeating the same mistakes perpetrated by Kagiomi Shizumiya and the remnants of the Yggdrasil Corporation.
- The events in the Underground City are basically an abridged version of Kamen Rider Gaim itself, with the characters fulfilling the same roles (Gaim is a noble idealist while Baron is a cynical social Darwinist and his arch-rival) and going through roughly the same events (Bravo starts off as an overpowering antagonist but undergoes a Heel–Face Turn).
- Honor Before Reason: Glasya believes so strongly in his ideals that he refuses to compromise them even when he knows it's a bad idea. When Aim comes along and says "This white Armored Rider is too strong, we need to team up to beat him!", Glasya refuses. Near the end of the play he insists on having a final battle with Aim, despite knowing full well that there are much more important things going on and that using the Sengoku Drivers will turn them into Inves, because he wants to prove the strength of his ideals. He loses.
- I'm Not a Hero, I'm...: Kagemasa angrily accuses Takatora of benefiting from his brother's death and passing himself off as the hero of Zawame City; Takatora honestly replies that Kouta was the one who saved the world, and that he himself didn't really do anything.
- Involuntary Battle to the Death: The rich nobles force the denizens of the Underground City to battle for their amusement, having provided them with Rider Systems and giving empty promises that the last man standing will be allowed to move to the upper city. By the time the story kicks in there are only three Rider Teams left (Orange Ride, Baroque Red, and Green Dolls), and Orange Ride is down to its last three members.
- Next Sunday A.D.: The story takes place "several years" after the events of Kamen Rider Gaim; the play itself was released five years after the TV series ended.
- Not Using the "Z" Word: Zig-zagged; the Trokian characters have heard of the term "Inves", but they more commonly call them "the infected". Takatora, on the other hand, just straight-up calls them "Inves".
- Nuclear Mutant: The microwave radiation emitted by the Scalar System somehow caused Masahito to mutate from a regular Inves into an Overlord.
- Outside-Context Problem: Takatora is an Outside-Context Hero, coming to the Trokia Republic from Japan and helping resolve the long-standing conflict by uniting the Armored Riders to fight against the nobles who oppress them rather than each other (as well as helping them fight an opponent that would have been too strong for any of them to handle).
- Paint It Black: The Armored Riders of the Trokia Republic, who are far more morally ambiguous than those from Zawame City, use prototype Sengoku Drivers that produce versions of Gaim, Baron, et al. with black undersuits. Since this already happened to Baron before in his Direct-to-DVD Gaiden movie, Glasya's Proto Baron suit is just a slight modification of Shura's Black Baron suit.
- Qurac: The Trokia Republic, which is shown to be a Fictional Counterpart to Kazakhstan.
- Rasputinian Death: Kagemasa gets shot in the gut, hangs on while refusing medical treatment, uses a suicide vest, somehow survives that too, and finally dies for real after being stabbed by his brother Masahito.
- Redemption Equals Death: Kagemasa spends most of the play bitterly despising Takatora for the death of his brother. However, after that same brother mortally wounds him and Takatora does his best to save him, Kagemasa uses his dying breath to give Takatora his Sengoku Driver so he can finally end the conflict. Later turns into Redemption Equals Life in the novelization when Aim and a bunch of other Trokian civilians find him on the verge of death and treat his wounds, with him repenting for his deeds by helping them rebuild.
- Reports of My Death Were Greatly Exaggerated: Everyone assumed that Masahito died eight years ago when the Scalar System was activated. In reality he had already transformed himself into an Inves via the flawed Sengoku Drivers and further mutated into an Overlord when the Scalar radiation hit him.
- Revenge: Kagemasa begins the story wanting to take revenge on Takatora, blaming him for the death of his brother Masahito. However, Masahito turns up alive...and he wants revenge on Takatora himself.
- Self-Made Orphan: Masahito murders his own father Kagiomi and assumes control of his organization. He takes it a step further by killing his younger brother Kagemasa as well.
- Soap Opera Disease: The Underground City's Armored Riders all seem to suffer from mysterious chest pains. These are the harbinger of their transformation into an Inves.
- The Social Darwinist: Glasya fulfills this role without having the same level of nuance or depth as his Expy source material Kaito Kumon; obviously a side character in a 2-hour play can't get as much Character Development as the Deuteragonist of a 47-episode TV series.
- Stock Footage: Takatora regaining his memories is generally represented by still photos from Gaim projected onto the large screen, and at one point a stock audio clip of Gaku Sano (Kouta) saying "Takatora" is played.
- Super Mode: Takatora receives his own version of Gaim's Kachidoki Arms from Kouta himself in time for the final battle.
- Taking You with Me: Kagemasa attempts to kill his brother Masahiko by grappling him while wearing a suicide vest. Unfortunately for him, a mere bomb isn't enough to kill an Overlord Inves.
- Theme Naming: All the new characters in the story, except for the Shizumiya family, derive their names from the 72 demons listed in the Ars Goetia.
- Underground City: The Trokia Republic has one, simply named "Underground City" (in English). It's said that about 80% of the country's population lives there, and the vast majority of the play takes place there.
- Unknown Character: The Orange Ride captain before Aym that disappeared. The novelization reveals his name as Simon and that he turned into the Byakko Inves that appears in the stageshow, similar to the fate of Yuya Sumii.
- Unwitting Test Subject: The entire Underground City is this, being subjects of Kagiomi Shizumiya's "experiments" with the incomplete Sengoku Drivers that slowly transform them into Inves.
- We Used to Be Friends: Takatora was friends with Masahito Shizumiya eight years before the events of the play, when they had similar personalities, but the fact that Takatora developed into a better person while Masahito stayed the same arrogant, selfish person he was before is just one of many reasons they oppose each other in the present.
