History Film / KamenRiderHeiseiGenerationsFinalBuildAndExAidWithLegendRiders

! Spoilers for all preceding ''Franchise/KamenRider'' entries, including ''Film/KamenRiderExAidTrueEnding', will be left unmarked ahead. Administrivia/YouHaveBeenWarned!

! All spoilers for ''Film/KamenRiderExAidTrueEnding'', ''Ghost RE:BIRTH: Kamen Rider Specter'', & ''Film/KamenRiderXKamenRiderWizardAndFourzeMovieWarUltimatum'' are unmarked. Administrivia/YouHaveBeenWarned!

! All spoilers for ''Film/KamenRiderExAidTrueEnding'' & ''Film/KamenRiderXKamenRiderWizardAndFourzeMovieWarUltimatum'' are unmarked. Administrivia/YouHaveBeenWarned!

! All spoilers for ''Film/KamenRiderExAidTrueEnding'' are unmarked. Administrivia/YouHaveBeenWarned!

* StartXToStopX: [[spoiler:Sento and Emu activate Enigma, which confuses the rest of the cast at first. However, during the final battle it turns out that by activating it early, they ensured that Mogami's fusion wasn't at full power and he could be defeated.]]

* WhenThePlanetsAlign: JK figures that the Enigma System in the World of Ex-Aid is at Amanogawa High School for this reason. The school has always been a nexus of Cosmic Energy, and Mogami set Enigma to activate at the moment the planets will align, which would give him incredible power.

** While the HandWave that Fourze's appearance in this takes place before he loses his powers in first act of ''Movie War Ultimatum'' is consistent with this movie's release date in 2017 when that part takes place, it indirectly contradicts the official statement by WordOfGod that Build's cameo in the post-credits scene of the ''True Ending'' movie takes place a year after the rest of the movie and the ''Ex-Aid'' series, since that would place the scene and this movie in 2018 after Fourze's powers are lost.

---

''Kamen Rider Heisei Generations FINAL: Build & Ex-Aid with Legend Riders'' is the ninth film in the ''Franchise/KamenRider'' franchise’s annual “Movie War” crossovers. Besides featuring Series/KamenRiderExAid and Series/KamenRiderBuild, this film also marks the return of several veteran Riders: [[Series/KamenRiderOOO OOO]], [[Series/KamenRiderFourze Fourze]], [[Series/KamenRiderGaim Gaim]], and [[Series/KamenRiderGhost Ghost]]. The name suggests that it was intended be the last Heisei era Movie War film due to diminishing box office returns and the then-upcoming abdication of Emperor Akihito (Heisei); what actually happened requires a bit of explaining. [[note]]As the movie was being developed, Akihito’s abdication was seen as almost certain, but a specific date wasn’t announced; nevertheless, the movie was titled as such due to ''Ex-Aid'' still having a bit to go when the abdication was approved by the Japanese Diet. The date was announced a week before this movie’s release as April 30, 2019; well into the run of the season after ''Build'' and, presumably, later than Toei expected. Ultimately, ''Kamen Rider Zi-O'' would be announced as the final Heisei Rider, along with the actual final entry in the Heisei-era film series: ''Heisei Generations FOREVER''.[[/note]]

Trouble strikes the parallel worlds of Build and Ex-Aid when a new enemy, Bugsters infused with Nebula Gas, appears and begins attacking the populace. Sento Kiryu, Kamen Rider Build, fights them off using a mysterious power he thought was only a dream, while Emu Hojo can’t become Kamen Rider Ex-Aid because a mysterious Kamen Rider appeared and drained his powers a week earlier. As the two worlds begin to collide, it’ll take the combined efforts of Sento, Emu, their allies and their Rider precursors to save everyone.

! Tropes exclusive to this movie:

* AlternateSelf: The movie’s BigBadDuumvirate are Kaisei Mogami, who's an amoral MadScientist in either world; the main difference is his employer (Foundation X in Ex-Aid’s world, self-employed after being fired by Touto Institute in Build’s world) and their personality (Mogami from Ex-Aid’s world is more eccentric while Build’s is more reserved).
* ApocalypseHow: Mogami’s plan is Class X, since the two Earths will be destroyed by the merger. It might go further than that, but the ramifications of the merger beyond Earth are never really discussed. The Mogamis don’t care either way, as by the time that happens they’ll be an immortal and omnipotent entity who can then become a MultiversalConqueror.
* BackFromTheDead: Ankh’s broken Core Medal enters his clone and allows him to possess it and take it over. Sadly it’s only temporary, but it gives Eiji further hope he can be restored permanently.

* BigDamnHeroes: The Legend Riders’ primary purpose in this movie seems to be coming in at the exact moment Sento, Emu, and the others need help.

** Foundation X returns in a major antagonistic role for the first time since ''Fourze'', their last appearance having been a cameo at the end of ''Ex-Aid''[=‘=]s “Beast Rider Squad” special.

** The events of this movie follow directly after Build’s EarlyBirdCameo in the post-credits scene of ''True Ending'', with him stealing Emu's powers in that movie being a plot point. Build’s encounter with Genm in the penultimate episode are also a plot point.
** ''Series/KamenRiderOOO'': Eiji is still WalkingTheEarth with Ankh’s broken Core Medal, and ends up being the one to tell the ''Ex-Aid'' and ''Build'' characters about Foundation X because [[Film/KamenRiderXKamenRiderFourzeAndOOOMovieWarMegaMax he’s dealt with them before]].
** ''Series/KamenRiderFourze'': This movie takes place in the “five years later” timeframe established by ''[[Film/KamenRiderXKamenRiderWizardAndFourzeMovieWarUltimatum Movie War Ultimatum]]'', and the former Kamen Rider Club members all have the jobs they had in that movie: Gentaro is a teacher, JK is a reporter, and the latter mentions that Yuki is an astronaut and Kengo is acting as her mission control.

* CatchPhrase: PlayedForLaughs: Before the final battle, Emu starts to deliver a variation of one of his phrases (“The fate of the two worlds… we’ll change it!”), but the last part is ruined by the other five Riders shouting ''their own'' Catch Phrases over him. They then have a brief squabble over it. Eiji is also retroactively given a catchphrase of his own for this scene despite lacking a proper PreAsskickingOneLiner in his own series.

** When Mogami summons copies of the Greeeds, Mezool’s copy is spawned while sitting on the shoulders of Gamel’s copy, a nod to the surrogate familial relationship the original characters had in ''OOO''.
** Ankh giving his Core Medals to Eiji so Eiji can use [=TaJaDor=] and the OOO Driver announcing the transformation with Ankh’s voice is something that happened in the finale of ''OOO''.

** The Ex-Aid riders, whose Gashat-based powers are the only things capable of harming the Nebula Bugsters, are unable to transform for significant portion of the movie because the Enigma’s activation caused them to malfunction.
** The Nebula Bugsters are invincible to attacks from any Riders other than the Ex-Aid ones, but because they’re fuel for the Enigma, the villains switch to using Guardian legions and replicated monsters right when most of the other past Riders are about to start fighting, giving them foes they can actually hurt.
** Emu spends most of the movie without access to his powers because Build stole them to create the Ex-Aid bottle when he appeared at the end of ''True Ending''. Without Hyper Muteki’s invincibility, the heroes end up struggling quite a bit.
** Sento doesn’t use [=RabbitTank=] Sparkling until the final battle because Banjō took it early on to try it out for himself, but ended up getting trapped in the World of Ex-Aid and unable to give it back until they reunite.
** A brief one for Eiji being unable to transform initially, as the movie acts as if the Core Medals being lost to oblivion after the finale of ''OOO'' is still in effect, despite him regaining the Core Medals in ''[=MegaMax=]'' and using them in subsequent appearances. Eiji ends up using Core Medals stolen from Foundation X’s Greeed copies in place of his usual ones.
* DynamicEntry: Kouta makes his entrance by destroying the Build World’s Enigma’s cloaking device with a jumping kick. ''Untransformed''.

** Played with regarding Build’s [=RabbitTank=] Sparkling form. Sento has already finished the TransformationTrinket at the start of the movie, but Banjou takes it because he wants to try using it. Then he gets sent to the World of Ex-Aid, and doesn’t get the opportunity to return the Fullbottle until the middle of the FinalBattle.

** Although he’s still nominally on the heroes’ side at this point, Kuroto’s hamminess and god complex have not slowed down one bit.
* FlashbackNightmare: At the start of the movie, Sento has a dream where Build attacks Ex-Aid and drains his power, but he doesn’t remember doing that. Eventually he figures out that it must have been Takumi Katsuragi using the Build Driver, and hypothesizes that holding onto the Ex-Aid Fullbottle allowed him to see the memory somehow. The movie doesn’t cover the true reason, namely [[spoiler:that Sento '''is''' Katsuragi]], which will be revealed in the [[Recap/KamenRiderBuildEp15JudgingSentoKiryu episode]] that immediately follows this movie.

* FusionDance: The Bi-Kaiser from the film’s final act; unlike the Hell Bros from ''Build'', the two Mogamis actually combine into a single being, with the transformation sequence showing half their bodies seemingly burning away before they merge and then the Kaiser suit appears.
* GodhoodSeeker: Kaisei Mogami’s ultimate plan is to become an immortal “emperor” by merging his two alternate selves into a single being. [[spoiler:Sento thwarts this by throwing off the timing]].
* GratuitousEnglish: The World of Ex-Aid version of Mogami is fond of saying, “funky,” which may be the reason the Nebula Steam Gun says it as well.

* HandWave: In order to patch a potential PlotHole between ''[[Film/KamenRiderXKamenRiderWizardAndFourzeMovieWarUltimatum Movie War Ultimatum]]'' and this movie[[note]]In the former, Gentaro destroys the Fourze Driver in order to motivate his student Saburo, yet he obviously has it in the latter[[/note]], ''FINAL''[=‘s=] director said that the events of this movie take place the day before ''Ultimatum''. (He also admits that he’d forgotten about that.)
* HistoryRepeats: [[Film/KamenRiderXKamenRiderFourzeAndOOOMovieWarMegaMax Once again]], a scientist for Foundation X ends up having their own universal conquest ambitions besides the group’s own goals and taking advantage of the Foundation’s resources to achieve them.

** Since the Nebula Bugster were made from a combination of two worlds’ elements, the only way to fight them is with a combination of those elements: Build has to use the Ex-Aid Fullbottles in order to harm them, while the Doctor Riders have to use a Build Gashat to protect their equipment from the Nebula Gas.

* NonIndicativeName: Despite its name, it’s ''not'' the final Heisei Generations movie. ''Kamen Rider Heisei Generations FOREVER'' is.
* NonSerialMovie: Unusually and aggressively averted. ''Build'' explicitly calls back to this movie when Seito brings in its own version of the Kaiser System used by the Mogamis, for ''Ex-Aid'' it acts as a side story that follows up on the ending of its summer movie and Build’s cameo in the penultimate episode, and most of the supporting Riders continue their post-series storylines from previous films.

** Gaim is, as in the end of his series, a god ruling a distant planet. Showcased when he is the only character who can go back and forth between the worlds without the Enigma, and manages to destroy the World of Build’s Enigma’s cloaking field with one kick (which took Fourze throwing two exploding Horoscope Zodiarts into it to destroy the field around the main universe’s version) while ''untransformed''.
** The Mogamis’ endgame is to become this and then become a MultiversalConqueror.
* PowerNullifier: The Enigma’s presence in the World of Ex-Aid emits slight traces of Nebula Gas that causes the Gamer Drivers and Gashats to malfunction. The ''Kamen Rider Build'' Gashat that Kuroto made is required to protect them from this while the Enigma is active.
* RedOniBlueOni: The two Mogamis. The blue oni is Kaisei Mogami from the World of Build, a SoftSpokenSadist and far more restrained than his World of Ex-Aid counterpart, the red oni, who definitely qualifies for EvilIsHammy. Fittingly, World of Build’s Mogami is the blue-colored Left Kaiser while the World of Ex-Aid’s Mogami is the red-colored Right Kaiser.

** While the HandWave that Fourze’s appearance in this takes place before he loses his powers in first act of ''Movie War Ultimatum'' is consistent with this movie’s release date in 2017 when that part takes place, it indirectly contradicts the official statement by WordOfGod that Build’s cameo in the post-credits scene of the ''True Ending'' movie takes place a year after the rest of the movie and the ''Ex-Aid'' series, since that would place the scene and this movie in 2018 after Fourze’s powers are lost.
** Eiji is implied to not have any Core Medals with him when he initially appears in this movie, and is only able to transform after Ankh pilfers some of Foundation X’s artificial Core Medals from Mogami’s Greeed clones. While this matches the status of the Medals at the end of ''OOO'', it seemingly ignores the fact that Eiji regained the Core Medals during ''Movie War [=MegaMax=]''. Further complicating this is that Eiji’s familiarity with Foundation X in this movie can only be explained by his previous encounter with them during ''[=MegaMax=]''.

* ShutUpHannibal: During the final battle, the Riders deliver a joint version of this to the fused Mogami, essentially telling him that he can’t beat them because a Kamen Rider’s power comes from their friends and the people they protect.
* StartXToStopX: [[spoiler:Sento and Emu activate Enigma, which confuses the rest of the cast at first. However, during the final battle it turns out that by activating it early, they ensured that Mogami’s fusion wasn’t at full power and he could be defeated.]]
* ThisCannotBe: Bikaiser’s response to Ex-Aid and Build overwhelming him and how they did it.
* TrappedInAnotherWorld: Kaisei Mogami uses the Enigma to trap Banjō in the World of Ex-Aid. Meanwhile, it’s revealed that after Build stole Emu’s powers, Parado chased him through the Enigma and landed in the World of Build, where he would spend the next two years while searching for Build. From the perspective of the World of Ex-Aid’s timeline, Emu’s powers and Parado have only been gone for a week, however.
* UnfinishedUntestedUsedAnyway: The ''Kamen Rider Build'' Gashat is untested and has some side-effects. Namely, the user gets shocked and ends up dropping their transformation after a while. The modified copies Takeru hands to the doctors after Kuroto’s initial use of it only mildly improve on this flaw, as he was on a short time limit to fix them and the glitches eventually kick in again.
* UnPerson: The ending credits feature a montage of still images from the five previous shows. These stills feature just about every important character from those shows, even if they didn't appear in this movie… with the exception of, in some shots, ''Fourze''[=‘s=] Yuki Jojima, whose absence is even more conspicuous because she was Gentaro’s best friend (and still gets name-dropped in this movie). Presumably this is because Yuki’s actress Fumika Shimizu (now going by Yoshiko Sengen after joining the controversial “Happy Science” religion) did an interview where she said she regretted appearing on the show. For comparison, Kengo Utahoshi still appears in the montage despite Ryuki Takahashi retiring from acting due to health concerns.
* UnusualEuphemism: Main!Mogami says the Nebula Gas Enigma uses ‘funked up’ the Gamer Drivers.

* WhateverHappenedToTheMouse: ''Kamen Rider Brave: ~Let's Survive! Revival of the Beast Riders Squad~'' hinted that Foundation X had been looking into the Gashats as a new investment opportunity. Whatever research they were planning on doing for that goes unmentioned in this movie, which focuses instead on the two Mogamis’ use of Foundation X’s resources for their own plans.

* YearInsideHourOutside: Time flows differently in the two worlds: according to Parado he’s been stranded in the World of Build for two years, but according to Emu he only left the World of Ex-Aid a week ago. As the two worlds begin to merge, time normalizes between them in order to avoid any weird complications.

* AGodAmI:
** Kaisei Mogami’s ultimate plan is to become an immortal “emperor” by merging his two alternate selves into a single being. [[spoiler:Sento thwarts this by throwing off the timing]].
** As per usual for ''Ex-Aid'', Kuroto Dan still insists upon being called a god, and Onari takes advantage of being a former priest to butter him up and obtain the Build Gashats the Doctor Riders need.

* MultiversalConqueror: The Mogamis intend to become this after [[FusionDance merging into Bikaiser]] and [[AGodIAm becoming an all powerful “Emperor”]].

''Kamen Rider Heisei Generations FINAL: Build & Ex-Aid with Legend Riders'' is the ninth film in the ''Franchise/KamenRider'' franchise's annual "Movie War" crossovers. Besides featuring Series/KamenRiderExAid and Series/KamenRiderBuild, this film also marks the return of several veteran Riders: [[Series/KamenRiderOOO OOO]], [[Series/KamenRiderFourze Fourze]], [[Series/KamenRiderGaim Gaim]], and [[Series/KamenRiderGhost Ghost]]. The name suggests that it was intended be the last Heisei era Movie War film due to diminishing box office returns and the then-upcoming abdication of Emperor Akihito (Heisei); what actually happened requires a bit of explaining. [[note]]As the movie was being developed, Akihito’s abdication was seen as almost certain, but a specific date wasn’t announced; nevertheless, the movie was titled as such due to ''Ex-Aid'' still having a bit to go when the abdication was approved by the Japanese Diet. The date was announced a week before this movie’s release as April 30, 2019; well into the run of the season after ''Build'' and, presumably, later than Toei expected. Ultimately, ''Kamen Rider Zi-O'' would be announced as the final Heisei Rider, along with the actual final entry in the Heisei-era film series: ''Heisei Generations FOREVER''.[[/note]]

** Sento doesn't use [=RabbitTank=] Sparkling until the final battle because Banjō took it early on to try it out for himself, but ended up getting trapped in the World of Ex-Aid and unable to give it back until they reunite.

** Although he’s still nominally on the heroes side at this point, Kuroto’s hamminess and god complex have not slowed down one bit.
* FlashbackNightmare: At the start of the movie, Sento has a dream where Build attacks Ex-Aid and drains his power, but he doesn’t remember doing that. Eventually he figures out that it must have been Takumi Katsuragi using the Build Driver, and hypothesizes that holding onto the Ex-Aid Fullbottle allowed him to see the memory somehow. The movie doesn't cover the true reason, namely [[spoiler:that Sento '''is''' Katsuragi]], which will be revealed in the [[Recap/KamenRiderBuildEp15JudgingSentoKiryu episode]] that immediately follows this movie.

* NonSerialMovie: Unusually aggressively averted. ''Build'' explicitly calls back to this movie when Seito brings in its own version of the Kaiser System used by the Mogamis, for ''Ex-Aid'' it acts as a side story that follows up on the ending of its summer movie and Build’s cameo in the penultimate episode, and most of the supporting Riders continue their post-series storylines from previous films.

* StartXToStopX: [[spoiler:Sento and Emu activate Enigma, which confuses the rest of the cast at first. However, during the final battle it turns out that by activating it early, they ensured that Mogami’s fusion wasn't at full power and he could be defeated.]]

* UnPerson: The ending credits feature a montage of still images from the five previous shows. These stills feature just about every important character from those shows, even if they didn't appear in this movie… with the exception of, in some shots, ''Fourze''[='s=] Yuki Jojima, whose absence is even more conspicuous because she was Gentaro's best friend (and still gets name-dropped in this movie). Presumably this is because Yuki's actress Fumika Shimizu (now going by Yoshiko Sengen after joining the controversial "Happy Science" religion) did an interview where she said she regretted appearing on the show. For comparison, Kengo Utahoshi still appears in the montage despite Ryuki Takahashi retiring from acting due to health concerns.
* UnusualEuphemism: Main!Mogami says the Nebula Gas Enigma uses 'funked up' the Gamer Drivers.

Trouble strikes the parallel worlds of Build and Ex-Aid when a new enemy, Bugsters infused with Nebula Gas, appears and begins attacking the populace. Sento Kiryu, Kamen Rider Build, fights them off using a mysterious power he thought was only a dream, while Emu Hojo can't become Kamen Rider Ex-Aid because a mysterious Kamen Rider appeared and drained his powers a week earlier. As the two worlds begin to collide, it’ll take the combined efforts of Sento, Emu, their allies and their Rider precursors to save everyone.

** Kaisei Mogami's ultimate plan is to become an immortal "emperor" by merging his two alternate selves into a single being. [[spoiler:Sento thwarts this by throwing off the timing]].

* AlternateSelf: The movie’s BigBadDuumvirate are Kaisei Mogami, who's an amoral MadScientist in either world; the only difference is his employer (Foundation X in Ex-Aid’s world, self-employed after being fired by Touto Institute in Build’s world) and their personality (Mogami from Ex-Aid is more eccentric while Build’s is more reserved).
* ApocalypseHow: Mogami's plan is Class X, since the two Earths will be destroyed by the merger. It might go further than that, but the ramifications of the merger beyond Earth are never really discussed. The Mogamis don’t care either way, as by the time that happens they'll be an immortal and omnipotent entity who can then become a MultiversalConqueror.
* BackFromTheDead: Ankh's broken Core Medal enters his clone and allows him to possess and take it over. Sadly it’s only temporary, but it gives Eiji further hope he can be restored permanently.

** Foundation X returns in a major antagonistic role for the first time since ''Fourze'', their last appearance having been a cameo at the end of ''Ex-Aid''[=‘=]s "Beast Rider Squad" special.

** ''Series/KamenRiderFourze'': This movie takes place in the "five years later" timeframe established by ''[[Film/KamenRiderXKamenRiderWizardAndFourzeMovieWarUltimatum Movie War Ultimatum]]'', and the former Kamen Rider Club members all have the jobs they had in that movie: Gentaro is a teacher, JK is a reporter, and the latter mentions that Yuki is an astronaut and Kengo is acting as her mission control.

* CatchPhrase: PlayedForLaughs: Before the final battle, Emu starts to deliver a variation of one of his phrases ("The fate of the two worlds… we'll change it!"), but the last part is ruined by the other five Riders shouting ''their own'' Catch Phrases over him. They then have a brief squabble over it. Eiji is also retroactively given a catchphrase of his own for this scene despite lacking a proper PreAsskickingOneLiner in his own series.

** When Mogami summons copies of the Greeeds, Mezool’s copy is spawned while sitting on the shoulders of Gamel's copy, a nod to the surrogate familial relationship the original characters had in ''OOO''.

* DimensionalTraveler: Kouta is capable of traveling between worlds completely of his own power. Justified, given he's literally a god and the Helheim Forest is interdimensional.

** The Ex-Aid riders, whose Gashat-based powers are the only things capable of harming the Nebula Bugsters, are unable to transform for significant portion of the movie because the Enigma's activation caused them to malfunction.
** The Nebula Bugsters are invincible to attacks from any Riders other than the Ex-Aid ones, but because they're fuel for the Enigma, the villains switch to using Guardian legions and replicated monsters right when most of the other past Riders are about to start fighting, giving them foes they can actually hurt.

** A brief one for Eiji being unable to transform initially, as the movie acts as if the Core Medals being lost to oblivion after the finale of ''OOO'' is still in effect, despite him regaining the Core Medals in ''[=MegaMax=]'' and using them in subsequent appearances. Eiji ends up using Core Medals stolen from Foundation X's Greeed copies in place of his usual ones.
* DynamicEntry: Kouta makes his entrance by destroying the Build World's Enigma's cloaking device with a jumping kick. ''Untransformed''.

** Played with regarding Build's [=RabbitTank=] Sparkling form. Sento has already finished the TransformationTrinket at the start of the movie, but Banjou takes it because he wants to try using it. Then he gets sent to the World of Ex-Aid, and doesn't get the opportunity to return the Fullbottle until the middle of the FinalBattle.

* FlawedPrototype: The Kamen Rider Build Gashat created by Kuroto Dan is untested, which causes it to deal backlash damage to its users and cancel their transformations after a while. This means that the Doctor Riders mostly end up fighting the Nebula Bugsters un-transformed with their Gashacon Weapons.

* HistoryRepeats: [[Film/KamenRiderXKamenRiderFourzeAndOOOMovieWarMegaMax Once again]], a scientist for Foundation X ends up having their own universal conquest ambitions besides the group's own goals and taking advantage of the Foundation's resources to achieve them.

** Since the Nebula Bugster were made from a combination of two worlds’ elements, the only way to harm them is with a combination of those elements: Build has to use the Ex-Aid Fullbottles, while the Doctor Riders have to use a Build Gashat.

* MultiversalConqueror: The Mogamis intend to become this after [[FusionDance merging into Bikaiser]] and [[AGodIAm becoming an all powerful "Emperor".]]

** While the HandWave that Fourze's appearance in this takes place before he loses his powers in first act of ''Movie War Ultimatum'' is consistent with this movie’s release date in 2017 when that part takes place, it indirectly contradicts the official statement by WordOfGod that Build’s cameo in the post-credits scene of the ''True Ending'' movie takes place a year after the rest of the movie and the ''Ex-Aid'' series, since that would place the scene and this movie in 2018 after Fourze’s powers are lost.

* ShutUpHannibal: During the final battle, the Riders deliver a joint version of this to the fused Mogami, essentially telling him that he can't beat them because a Kamen Rider’s power comes from their friends and the people they protect.

* ThisCannotBe: Bikaiser’s response to Ex-aid and Build overwhelming him and how they did it.

''Kamen Rider Heisei Generations FINAL: Build & Ex-Aid with Legend Riders'' is the ninth film in the ''Franchise/KamenRider'' franchise's annual "Movie War" crossovers. Besides featuring Series/KamenRiderExAid and Series/KamenRiderBuild, this film also marks the return of several veteran Riders: [[Series/KamenRiderOOO OOO]], [[Series/KamenRiderFourze Fourze]], [[Series/KamenRiderGaim Gaim]], and [[Series/KamenRiderGhost Ghost]]. The name suggests that it was intended be the last Heisei era Movie War film due to diminishing box office returns and the then-upcoming abdication of Emperor Akihito (Heisei); what actually happened requires a bit of explaining. [[note]]As the movie was being developed, Akihito's abdication was seen as almost certain, but a specific date wasn't announced; nevertheless, the movie was titled as such due to ''Ex-Aid'' still having a bit to go when the abdication was approved by the Japanese Diet. The date was announced a week before this movie's release as April 30, 2019; well into the run of the season after ''Build'' and, presumably, later than Toei expected. Ultimately, ''Kamen Rider Zi-O'' would be announced as the final Heisei Rider, along with the actual final entry in the Heisei-era film series: ''Heisei Generations FOREVER''.[[/note]]

Trouble strikes the parallel worlds of Build and Ex-Aid when a new enemy, Bugsters infused with Nebula Gas, appears and begins attacking the populace. Sento Kiryu, Kamen Rider Build, fights them off using a mysterious power he thought was only a dream, while Emu Hojo can't become Kamen Rider Ex-Aid because a mysterious Kamen Rider appeared and drained his powers a week earlier. As the two worlds begin to collide, it'll take the combined efforts of Sento, Emu, their allies and their Rider precursors to save everyone.

* AlternateSelf: The movie's BigBadDuumvirate are Kaisei Mogami, who's an amoral MadScientist in either world; the only difference is his employer (Foundation X in Ex-Aid's world, self-employed after being fired by Touto Matter Research in Build's world) and their personality (Mogami from Ex-Aid is more eccentric while Build's is more reserved).
* ApocalypseHow: Mogami's plan is Class X, since the two Earths will be destroyed by the merger. It might go further than that, but the ramifications of the merger beyond Earth are never really discussed. The Mogamis don't care either way, as by the time that happens they'll be an immortal and omnipotent entity who can then become a MultiversalConqueror.
* BackFromTheDead: Ankh's broken Core Medal enters his clone and allows him to possess and take it over. Sadly it's only temporary, but it gives Eiji further hope he can be restored permanently.

* BigBadDuumvirate: The Kaisei Mogamis are responsible for everything and the main villain.
* BigDamnHeroes: The Legend Riders' primary purpose in this movie seems to be coming in at the exact moment Sento, Emu, and the others need help.

** Foundation X returns in a major antagonistic role for the first time since ''Fourze'', their last appearance having been a cameo at the end of ''Ex-Aid''[='=]s "Beast Rider Squad" special.

** The events of this movie follow directly after Build's EarlyBirdCameo in the post-credits scene of ''True Ending'', with him stealing Emu's powers in that movie being a plot point.
** ''Series/KamenRiderOOO'': Eiji is still WalkingTheEarth with Ankh's broken Core Medal, and ends up being the one to tell the ''Ex-Aid'' and ''Build'' characters about Foundation X because [[Film/KamenRiderXKamenRiderFourzeAndOOOMovieWarMegaMax he's dealt with them before]].

** Foundation X still has the technology to create their own Core Medals and Astro Switches, as they did in ''[[Film/KamenRiderXKamenRiderFourzeAndOOOMovieWarMegaMax Movie War Mega Max]]'', which lets them create copies of the Greeed and Horoscopes.

** When Mogami summons copies of the Greeeds, Mezool's copy is spawned while sitting on the shoulders of Gamel's copy, a nod to the surrogate familial relationship the original characters had in ''OOO''.
** Ankh giving his Core Medals to Eiji so Eiji can use [=TaJaDor=] and the OOO Driver announcing the transformation with Ankh's voice is something that happened in the finale of ''OOO''.
* DimensionalTraveler: Kouta is capable of traveling between worlds completely of his own power. Justified, given he's literally a god and the Helhiem Forest is interdimensional.

** Emu spends most of the movie without access to his powers because Build stole them to create the Ex-Aid bottle when he appeared at the end of ''True Ending''. Without Hyper Muteki's invincibility, the heroes end up struggling quite a bit.

** Hyper Muteki ends up being this since Emu spends much of the movie without access to his powers until Sento gives him the Doctor and Game bottles before the climax

** Although he's still nominally on the heroes side at this point, Kuroto's hamminess and god complex have not slowed down one bit.
* FlashbackNightmare: At the start of the movie, Sento has a dream where Build attacks Ex-Aid and drains his power, but he doesn't remember doing that. Eventually he figures out that it must have been Takumi Katsuragi using the Build Driver, and theorizes that holding onto the Ex-Aid Fullbottle allowed him to see the memory somehow. The movie doesn't cover the true reason, namely [[spoiler:that Sento '''is''' Katsuragi]], which will be revealed in the [[Recap/KamenRiderBuildEp15JudgingSentoKiryu episode]] that immediately follows this movie.

* FusionDance: The Bi-Kaiser from the film's final act; unlike the Hell Bros from ''Build'', the two Mogamis actually combine into a single being, with the transformation sequence showing half their bodies seemingly burning away before they merge and then the Kaiser suit appears.
* GratuitousEnglish: The World of Ex-Aid version of Mogami is fond of saying “funky,” which may be the reason the Nebula Steam Gun says it as well.

** Since the Nebula Bugster were made from a combination of two worlds' elements, the only way to harm them is with a combination of those elements: Build has to use the Ex-Aid Fullbottles, while the Doctor Riders have to use a Build Gashat.

* NonIndicativeName: Despite its name, it's ''not'' the final Heisei Generations movie. ''Kamen Rider Heisei Generations FOREVER'' is.
* NonSerialMovie: Unusually aggressively averted. ''Build'' explicitly calls back to this movie when Seito brings in its own version of the Kaiser System used by the Mogamis, for ''Ex-Aid'' it acts as a sidestory that follows up on the ending of its summer movie, and most of the supporting Riders continue their post-series storylines from previous films.
* OneManArmy: OOO, Fourze, Gaim, and Ghost vs a ''gigantic'' army of Guardians. The Guardians never had a chance.

** Eiji is implied to not have any Core Medals with him when he initially appears in this movie, and is only able to transform after Ankh pilfers some of Foundation X’s artificial Core Medals from Mogami's Greeed clones. While this matches the status of the Medals at the end of ''OOO'', it seemingly ignores the fact that Eiji regained the Core Medals during ''Movie War [=MegaMax=]''. Further complicating this is that Eiji’s familiarity with Foundation X in this movie can only be explained by his previous encounter with them during ''[=MegaMax=]''.

* FlawedPrototype: The Kamen Rider Build Gashat created by Kuroto Dan is untested, which causes it to deal backlash damage to its users and cancel their transformations after a while. This means that the Doctor Riders mostly end up fighting the Nebula Bugsters un-transformed with their Gashacon Weapons. Enigma itself is a flawed prototype of what ultimately becomes the plot of Build's endgame.

* GratuitousEnglish: The World of Ex-Aid version of Mogami is fond of saying "funky", which may be the reason the Nebula Steam Gun says it as well.
* HalfTheManHeUsedToBe: The World of Build version of Mogami had the left of his body replaced with cybernetics after [[spoiler:Enigma was activated by accident when he struggled with Takumi Katsuragi and the energy fried him]]. When the two finally merge, both get half their body vaporized and while the other merges with their alternate self's remaining half. Given its the same half,it's likely pat of Enigma's function.
* HandWave: In order to patch a potential PlotHole between ''[[Film/KamenRiderXKamenRiderWizardAndFourzeMovieWarUltimatum Movie War Ultimatum]]'' and this movie[[note]]In the former, Gentaro destroys the Fourze Driver in order to motivate his student Saburo, yet he obviously has it in the latter[[/note]], ''FINAL''[='s=] director said that the events of this movie take place the day before ''Ultimatum''. (He also admits that he’d forgotten about that.)

** Nebula Gas is shown to have a negative effect on the Gamer Drivers and Gashats. Parado also becomes weak when he uses the Gamer Fullbottle to communicate with Emu.

* NonindicativeName: Despite it's name, it's ''not'' the final Heisei Generations movie as ''Kamen Rider Heisei Generations FOREVER'' is scheduled for a 12/22/18 release.

** Gaim is, as in the end of his series, a god ruling a distant planet. Showcased when he is the only character who can go back and forth between the worlds without the Enigma, and manages to destroy the Build verse's Enigma's cloaking field with one kick (which took Fourze throwing two exploding Horoscope Zodiarts into it to destroy the field around the main universe's version) while ''untransformed''.
** The Mogamis' endgame is to become this and then become a MultiversalConqueror.
* PowerNullifier: The Enigma's presence in the World of Ex-Aid emits slight traces of Nebula Gas that causes the Gamer Drivers and Gashats to malfunction. The ''Kamen Rider Build'' Gashat that Kuroto made is required to protect them from this while the Enigma is active.
* RedOniBlueOni: The two Mogamis. The blue oni is Kaisei Mogami from the World of Build, a SoftSpokenSadist and far more restrained than his World of Ex-Aid counterpart, the red oni, who definitely qualifies for EvilIsHammy. Fittingly, World of Build's Mogami is the blue-colored Left Kaiser while the World of Ex-Aid's Mogami is the red-colored Right Kaiser.

** While the HandWave that Fourze's appearance in this takes place before he loses his powers in first act of ''Movie War Ultimatum'' is consistent with this movie's release date in 2017 when that part takes place, it indirectly contradicts the official statement by WordOfGod that Build's cameo in the post-credits scene of the ''True Ending'' movie takes place a year after the rest of the movie and the ''Ex-Aid'' series, since that would place the scene and this movie in 2018 after Fourze's powers are lost.
** Eiji is implied to not have any Core Medals with him when he initially appears in this movie, and is only able to transform after Ankh pilfers some of Foundation X's artificial Core Medals from Mogami's Greeed clones. While this matches the status of the Medals at the end of ''OOO'', it seemingly ignores the fact that Eiji regained the Core Medals during ''Movie War [=MegaMax=]''. Further complicating this is that Eiji's familiarity with Foundation X in this movie can only be explained by his previous encounter with them during ''[=MegaMax=]''.

* ShutUpHannibal: During the final battle, the Riders deliver a joint version of this to the fused Mogami, essentially telling him that he can't beat them because a Kamen Rider's power comes from their friends and the people they protect.
* StartXToStopX: [[spoiler:Sento and Emu activate Enigma, which confuses the rest of the cast at first. However, during the final battle it turns out that by activating it early, they ensured that Mogami's fusion wasn't at full power and he could be defeated.]]
* ThisCannotBe: Bikaiser's response to Ex-aid and Build overwhelming him and how they did it.
* TrappedInAnotherWorld: Kaisei Mogami uses the Enigma to trap Banjō in the World of Ex-Aid. Meanwhile, it's revealed that after Build stole Emu's powers, Parado chased him through the Enigma and landed in the World of Build, where he would spend the next two years while searching for Build. From the perspective of the World of Ex-Aid's timeline, Emu's powers and Parado have only been gone for a week, however.

* WhateverHappenedToTheMouse: ''Kamen Rider Brave: ~Let's Survive! Revival of the Beast Riders Squad~'' hinted that Foundation X had been looking into the Gashats as a new investment opportunity. Whatever research they were planning on doing for that goes unmentioned in this movie, which focuses instead on the two Mogamis' use of Foundation X's resources for their own plans.

* YearInsideHourOutside: Time flows differently in the two worlds: according to Parado he's been stranded in the World of Build for two years, but according to Emu he only left the World of Ex-Aid a week ago. As the two worlds begin to merge, time normalizes between them in order to avoid any weird complications.