[[quoteright:220:http://static.tvtropes.org/pmwiki/pub/images/220px_fourze_&_ooo_mega_max.jpg]]
''Franchise/KamenRider × Series/KamenRiderFourze & [[Series/KamenRiderOOO OOO]]: Movie War Mega Max'' is the third Movie War movie. Premiered in Japanese theatres on December 10, 2011.

In need of the following [[Main/NeedsWikiMagicLove Wiki Magic Love]]:
* Administrivia/NeedsABetterDescription: Short

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!! This movie contains examples of the following tropes:
* AGodAmI: [[spoiler:Lem Kannagi once he becomes the Super Galaxy King]].
* AllThereInTheManual:
** The names of Michal's Kamen Rider forms. The evil form that uses core medals is called Kamen Rider Poseidon, and the good form created from the water-powered belt is called Kamen Rider Aqua.
*** The name of Michal's jet ski is "Aqua Miraider".
** The names of Kannagi's [[CoDragons two assistants]] are Solaris and Katal.
*** Katal's Mutamid form is called Suddendath.
* AlmostKiss: Gentarō and Nadeshiko are about to kiss on the moon, but the helmets of their spacesuits get in the way. Nadeshiko [[BatmanCanBreatheInSpace takes hers of]], but luckily, Gentarō realizes that there's something wrong about her before he can follow suit.
* BatmanCanBreatheInSpace: Nadeshiko being able to survive on the moon without her helmet on is how Gentarō learns that she's not a normal girl.
* BigBad: Lem Kannagi of [[Series/KamenRiderDouble Foundation X]].
** BigBadEnsemble: Lem Kannagi is the BigBad for most of the story, but his only appearance in the OOO portion is at the end. Poseidon is the BigBad of that portion of the movie instead.
* BigDamnHeroes: Date and Gotō show up on jet skis to help Eiji and Ankh in the fight against Poseidon, having used painkillers to briefly recover from hospitalization.
* BloodKnight: Poseidon's motive for traveling through time is to enjoy battles against the heroes and warriors of various eras.
* TheCameo: Jun Kazu, the final boss of ''Series/KamenRiderDouble'', appears in archived footage from the reunion special, as do Katsumi Daidō and the members of NEVER, again through archived footage from TheMovie.
* CoDragons: Solaris and Katal (Suddendath) to Kannagi.
* ContinuityNod: Tons given that this is a crossover (See below).
** In the [[ReCut Director's Cut]], Gentaro does his own take on [[KamenRiderStronger Kamen Rider Stronger's]] trademark introduction speech before his fight with the Dustards at Amanogawa High.
** It's implied that Foundation X backed the Kougami Foundation's research on Core Medals.
** Shotaro still uses the Lost Driver, though it's unclear if it's [[spoiler:the one left to him by Skull or the one left to him by Philip after his "death"]].
** Both crossover [[EarlyBirdCameo cameos]] in ''Kamen Rider W Forever'' and ''Kamen Rider OOO Wonderful'' are referenced.
** Not to mention that Shotaro references Eiji's exclamation that "Riders look out for each other" from ''Kamen Rider W Forever''.
** When Philip is giving exposition about Foundation X, he brings up NEVER, the main antagonists of the summer movie for ''Series/KamenRiderDouble''. This also includes archival footage from that movie, as well as footage from the reunion special, ''Kamen Rider Double Returns: Kamen Rider Eternal''.
* {{Crossover}}: As the name of the movie suggests, it's a crossover between ''Series/KamenRiderFourze'' and ''Series/KamenRiderOOO''. However, [[Series/KamenRiderDouble Kamen Rider Double and Foundation X]] are featured as well, uniting the first three leading riders of the post-Decade Heisei era. In the wake of ''[[Film/OOODenOAllRidersLetsGoKamenRiders OOO, Den-O, All Riders: Let's Go Kamen Riders]]'', 2011 being the fortieth anniversary year of the series, the original seven Kamen Riders ([[Series/KamenRider Riders 1, 2]], [[Series/KamenRiderV3 V3, Riderman]], [[Series/KamenRiderX X]], [[Series/KamenRiderAmazon Amazon]], and [[Series/KamenRiderStronger Stronger]]) play a major role as well, where they are now known as the Seven Legendary Riders.
* CoDragons: Solaris and Katal (Suddendath) to Kannagi.
* EarlyBirdCameo: As each Movie War movie has featured the introduction of the upcoming [[SixthRanger Secondary Rider]] of the current show, Kamen Rider Meteor makes his first appearance at the end of the movie.
* [[EleventhHourRanger Eleventh Hour Rider]]: [[spoiler:Kamen Rider Aqua returns from the future to help the Riders against Foundation X's forces, and give Eiji the Super [=TaToBa=] medals.]]
* EnemyWithin: Michal Minato's form as Poseidon. [[spoiler:Poseidon eventually becomes an EnemyWithout]].
* TheGlassesComeOff: Lem Kannagi does this when [[spoiler:he reveals his betrayal of Foundation X]].
* ForHappiness: Shotaro is quick to voice how unimpressed he is with Gentaro - and just as quick to change his mind when he learns they have this exact same motive.
* HamToHamCombat: Shotaro and Gentaro, with Eiji and Philip looking on in (respectively) bafflement and amusement.
* HoistByTheirOwnPetard: The Super Galaxy King fired a blast of Cosmic Energy at OOO and Fourze, but [[spoiler:Nadeshiko allowed Fourze to absorb it himself and defeat Kannagi]].
* KissingDiscretionShot: [[spoiler:Gentarō and Nadeshiko's kiss after the defeat of Kannagi]].
* LegacyCharacter: Similar to how the finale of ''Series/KamenRiderDouble'' established that there can be multiple copies of the same [[TransformationTrinket Gaia Memory]], four members of Foundation X are shown using Zodiarts Switches to transform into copies of previously defeated Zodiarts.
* LegionOfDoom: Foundation X uses the research its agents gathered to build an army consisting of various MonstersOfTheWeek as well as mooks from the three series ''Fourze'', ''OOO'' and ''W'', alongside monsters of the BigBad's own design, called "Mutamids". They're not actually the same monsters from their original series, but it's [[PropRecycling an excuse to reuse monster suits]].
* MacguffinGirl: Nadeshiko.
* TheMagicComesBack: [[spoiler: At the end of ''OOO'', all of the Core Medals, with the exception of Ankh's personal Core Medal, were thought to have been lost to oblivion in the vortex that destroyed Dr. Maki and the Medal Vessel. In this movie, it's revealed that the Core Medals were sent into the future, where they ended up being absorbed by Michal Minato, turning his Poseidon identity into a SuperpoweredEvilSide. When Poseidon traveled into the past, the Core Medals were with him, allowing Ankh to retrieve them so Eiji may become OOO once again]].
* MakeMeWannaShout: Kannagi's Mutamit experiments have given him the ability to do this, which he uses to repel enemies, ambush Eiji and Hina, [[spoiler:capture Nadeshiko]], and [[spoiler:kill his commanding officer once he betrays Foundation X]].
* MenDontCry: Gentaro claims that a man is only allowed to cry if he's [[ArsonMurderAndJaywalking lost his wallet]] or been dumped.
* {{Mooks}}: Through their research into the Gaia Memories, O Medals, and Cosmic Energy, as well as their partnerships with the [[Series/KamenRiderDouble Museum]] and Gamou, Foundation X boasts a vast foot soldier army of Masquerade Dopants (with a white suited variant transformed from Foundation X members using Gaia Memories), Waste Yummies, and Dustards. Poseidon also creates his own Waste Yummy army in OOO's portion by channeling the power of Uva's Core Medals, while in Fourze's portion Virgo leads a force of Dustards against Fourze and Nadeshiko as a favor from Gamou to Foundation X.
* MythologyGag:
** The Seven Legendary Riders are battling Foundation X in various countries. Back in the old days, when a Rider's predecessors would always appear in the final arc to help out, where did the guest star Riders say they were coming from? ''Fighting the evil organization's branches in other countries.'' This goes all the way back to the very first series, when Takeshi Hongo - his actor having recovered from the injury that necessitated Hayato Ichimonji's introduction - returned midseries. Fighting Shocker overseas is where he'd been. The only difference is this time we ''see'' the Seven Legendary Riders' overseas battles before they return to Japan to fight alongside the current heroes.
** Michal's transformation into Aqua is reminiscent of Kamen Rider #1's previous transformation sequence, but with water and a jet ski instead of wind and a motorcycle.
** [=V3=] fighting the [=ClayDoll=] Dopant may refer to his backstory of [[StuffedIntoTheFridge losing his family]], including his little sister, and the fact that the original [=ClayDoll=] Dopant's civilian identity, Wakana Sonozaki, was the younger sister of the Sonozaki [[BigScrewedUpFamily family]].
** The Super Galaxy King is a reference to the BigBad of ''Eight Riders vs. Galaxy King'', TheMovie for ''Skyrider'', which had him team up with the same Legendary Seven Riders who appear in this movie. TheDragon to him, Suddendath, is a homage to Suddendas, who was TheDragon to Galaxy King.
** Nadeshiko's given name, Yuriko, is a homage to [[Series/KamenRiderStronger Yuriko Misaki]], Stronger's partner and ImpliedLoveInterest. Nadeshiko herself is the LoveInterest to Gentarō, who dresses up as Stronger in this movie. [[spoiler:This reference also extends to the fact that they both die, though Nadeshiko comes BackFromTheDead in the next Movie War.]]
** The Rocket Super-1 Switch is a subtle reference to ''Series/KamenRiderSuper1'', who also had an outer space motif like Fourze does.
* OneManArmy: There are many scenes of a character fighting several Mooks alone, or with help from, at most, one other person who qualifies for this trope themselves. The best examples would be Stronger, who is the only one of the Legendary Seven Riders to fight alone in the beginning montage (as well as the only one fighting all three types of the Mooks they fought) and OOO and Fourze taking on the army of Mooks while their theme songs play.
* OneWingedAngel: [[spoiler:Lem Kannagi's master plan is to achieve this, becoming the Super Galaxy King]].
* PowerCopying: SOLU is able to copy data from pretty much anything, including devices and people, and can even improve on whatever it copies. [[spoiler:A SOLU sample copying the real Nadeshiko Misaki is how the Nadeshiko who Gentarō meets comes to existence. It's also the reason she can transform her own Driver based on his, and the Rocket Super-1 switch is made of SOLU replicating the Rocket Switch and upgrading on it.]]
* ThePowerOfLove: Gentarō's love for Nadeshiko [[spoiler:causes her to develop emotional capacity and human-level sapience beyond her initial BlankSlate personality as a blob of SOLU]]. In the final battle, [[spoiler:Nadeshiko helps Gentarō by letting him absorb the Cosmic Energy that the Super Galaxy King was using against him and OOO]].
* SealedGoodInACan: The Seven Legendary Riders are sealed inside Fourze and OOO's [[TransformationTrinket transformation trinkets]] by Kannagi. 1, 2, V3 and Riderman are trapped within Astro Switches while X, Amazon and Stronger trapped inside Core Medals. They are freed when Fourze and OOO perform a Limit Break and a Scanning Charge respectively.
* SenpaiKouhai: Gentarō addresses Shotarō and Philip as his and OOO's Senpai, which they take a liking to.
* StarCrossedLovers: Gentarō doesn't take it very well when Kengo insists to him that he can't date Nadeshiko because she's basically [[spoiler:a shapeshifting puddle of space slime]]. He changes his mind eventually.
* TheStarscream: [[spoiler:Lem Kannagi was the head of a Foundation X project to control the world's energy supplies, but he used those resources to instead attempt to conquer the galaxy.]]
* SuperMode: OOO's Super [=TaToBa=] Combo and Fourze's Rocket States.
** SuperpoweredEvilSide: Poseidon was intended to be a SuperMode for Aqua, but became this when Poseidon's Core Medals developed sentience upon Michal's [[spoiler:absorption of the Core Medals and Cell Medals of OOO, Dr. Maki, and the Medal Vessel]].
* ThemeMusicPowerUp: All over the place.
** The montage of the Legendary Seven Riders fighting evil around the world is accompanied by a [[Main/AwesomeMusic badass]] {{Leitmotif}} that is an instrumental, orchestral rock remix of "Fight! Seven Riders", which was their theme song when they appeared in the BatFamilyCrossover finale of ''Series/KamenRiderStronger''. It gets played again when they take on the Greeeds and Dopants.
** Shotarō fighting Foundation X as Kamen Rider Joker uses his {{Leitmotif}} from ''Kamen Rider Double Forever''.
** Double taking on the Zodiarts has "W-B-X", the opening theme song of ''Series/KamenRiderDouble''.
** When OOO and Fourze are battling the Masquerade Dopants, Waste Yummies, and Stardust Ninja Dustards together, their opening theme songs, "Anything Goes!" and "Switch On!" respectively, play consecutively.
* ThisCannotBe: Lem Kannagi after his defeat.
* TimeStandsStill: The Super Galaxy King is able to do this by taping into the power of Poseidon's time-displaced Core Medals from the future. [[spoiler:OOO can counter this with the Super [=TaToBa=] Combo, whose Medals are also from the future.]]
* TookALevelInBadass: Since the end of his [[Series/KamenRiderOOO season]], Eiji has become noticeably more skilled in combat as a civilian, without needing to transform. [[spoiler:Ankh as well]].
* TrashTheSet: Being the finale to [=OOO=], Cous Coussier is trashed following an attack by Yummies on Eiji and Ankh. Chiyoko tells them [[CrowningMomentOfAwesome that it will open just the same as it always has the next day.]]
* TheUnfought: One of the Mutamits, Solaris, briefly demonstrates feline attributes during Foundation X's meeting with Gamō. Unlike Katal, she never assumes her full Mutamit transformation, instead opting for turning into the Unicorn Zodiarts to fight the heroes.
* WhatMeasureIsANonHuman: Kengo's original attitude to [[spoiler:Nadeshiko, viewing her as nothing more than a technological pseudo-organism that mimics human behaviour rather than a person with feelings]]. [[spoiler:When ThePowerOfLove from Gentarō causes her to develop the capacity for genuine emotion,]] Kengo changes his mind about it.
* WhyDidItHaveToBeSnakes: Ironically, despite being a water-themed Rider, Michal is hydrophobic. [[spoiler:He manages to overcome it in the end.]]
* TheWorfEffect:
** Birth and Proto-Birth lose handily to Poseidon.
** The Seven Legendary Riders are hit with this to show how dangerous Foundation X's threat is here in the movie.