[[AC: ''Manga/{{Bleach}}'']]
* In ''FanFic/HogyokuExMachina'', Yoruichi is surprised when she finds out that the Vizards fought alongside Soul Society against [[BigBad Aizen]] in the [[TimeTravel original timeline]], since they have no reason to like them. [[TheSmartGuy Ishida]] suggests it was because of this trope.

[[AC: ''Comicbook/{{Batman}}'']]
* In Fanfic/AngelOfTheBat, Stephanie/Spoiler struggles to bring Red Hood to her cause of [[spoiler: saving Cassie]] because it will mean they will be closer to bringing down their mutual enemy The Seraphim. It doesn’t work [[spoiler: at first. Batman eventually breaks Jason’s resistance personally.]]

[[AC: ''ComicStrip/CalvinAndHobbes'']]
* [[CardCarryingVillain Dr. Brainstorm]] tries to {{def|iedTrope}}y this twice in ''Fanfic/CalvinAndHobbesTheSeries''. Both times, he ends up playing it straight.

[[AC: ''WesternAnimation/ChipNDaleRescueRangers'']]
* ''[[Fanfic/TheNowakverse Under the Bridge]]'': Widget has taken several attempts at killing Gadget. Now Chip calls her on her submarine ''Albacore'' on the radio, alerting her that Gadget is out to attack and sink ''Albacore'' with a self-made, air-dropped torpedo. But the call comes in time: A young squirrel from Widget's crew named Andy injured an ankle on an unprotected chain, and now Widget needs Gadget and her aircraft to take him to a hospital. Meanwhile, when Widget comforts Andy, this also helps trigger her HeelFaceTurn.

[[AC: ''Literature/ChroniclesOfNarnia'']]
* In ''FanFic/{{Carpetbaggers}}'', when the newly-crowned Pevensies need backup to fight a horde of the Witch’s creatures, they recruit the rebels who were holed up in the castle bullying and blackmailing local Narnians.

[[AC: CrossOver]]
* ''Fanfic/ThousandShinji'':
** Discussed. Asuka suggests that she and Rei should team up (because Shinji enjoys annoying Asuka and Rei likes annoying Shinji), citing the "The enemy of my enemy is my friend" sentence. Rei gets surprised because Shinji has a different version: "The enemy of my enemy dies next."
** Nothing less than an overwhelmingly bad situation could possibly force [[spoiler:the ''TabletopGame/{{Warhammer 40000}} gods'']] to work together. We're talking a reluctant agnostic/atheist turned God-Emperor of Man, the Four Ruinous Powers (whom are sufficiently powerful that the *only* reason they haven't taken over the world is because they A) *HATE* each other, B) like it just the way it is, and C) already have...), Gork & Mork (the deities of a bunch of genetically engineered fungal bio-weapon), and the Eldar Pantheon (and let's not talk about all the shit they got up to with each other!
* This happens in the Naruto/Justice League crossover ''Fanfic/ConnectingTheDots'' when Naruto and Sasuke team up against a REALLY big threat.
* ''FanFic/BurningBlack'': Anti-Cosmo, and by proxy every anti-fairy he commands, allies with Team Turner against Remy and [[spoiler:[[TheManBehindTheMan the Pixies]]]] in Act 3. He even outlaws the use of bad luck on Timothy directly; indirect bad luck is still fair game. The relationship is creeping into FriendlyEnemy territory, which makes Cosmo and Wanda very nervous as Timmy's exposure to anti-fairies affects his personality and allows him to use black magic while giving him immunity to anti-magic waves.
* In ''FanFic/{{Fractured}}'', a ''MassEffect''[=/=]''StarWars''[[spoiler:[=/=]''[=Borderlands=]'']] [[MassiveMultiplayerCrossover crossover]] and its sequel ''[[FanFic/SovereignGFCOrigins Origins]]'', this is attempted several times. Whether it works is another matter.
** Unlike [[VideoGame/MassEffect3 canon]], Samantha Shepard is ''not'' able to pull this off with the whole galaxy when the [[EldritchAbomination Reapers]] arrive, thanks to a TechnologyUplift [[NiceJobBreakingItHero gone wrong]] that causes [[FantasticRacism existing tensions]] to get worse rather than fade away in the face of a common foe.
** The Citadel Council attempts to manage this through Aria T'Loak in the Terminus by having her unite the various mercenary factions to fight [[spoiler:Flood]]. It works in that the mercenaries cooperate, but their efforts fall flat.
** Garrus Vakarian ''tries'' to accomplish this by [[BatmanGambit causing an arms race]] in the CorporateWarfare taking place around him, but it fails on two fronts: the corporations distrust each other and there [[YouRequireMoreVespeneGas aren't enough resources]] for this to work even if they did.
** The heroes tend to view Sarah this way initially--she did kill millions of people even if it was for a [[WellIntentionedExtremist good reason]]. [[spoiler:Flood invasions are generally bad.]]
* ''Fanfic/SOE2LoneHeirOfKrypton'': The first time that ''[[Comicbook/{{Supergirl}} Asuka]]'' and ''[[Comicbook/WonderGirl Rei]]'' are on the same battlefield is during the Brainiac crisis. The first time they have to work together is when Parasite kidnaps them both to use as "power chargers". Asuka finds a lot of respect for Wonder Girl on that day-time will tell if they become FireForgedFriends.
* ''FanFic/ADarkKnightOverSinCity'' features Franchise/{{Batman}} and the [[AntiHero anti-heroes]] from SinCity teaming up together and with other criminals in order to achieve their goals.
* ''FanFic/AShadowOfTheTitans'': Jinx briefly teams up with the Titans after Mumbo captures both Jade and Starfire and forces them to be his "assistants". Jinx describes it as "sharing a mutual problem", and as soon as Mumbo is defeated she grabs Jade and runs off.
** The possible BadFuture glimpsed in the "[[MindScrew Destiny]]" interlude has another apparent example: [[spoiler: whatever "[[NamesToRunAwayFromReallyFast Omega]]" is, it's so bad that the Demon Sorcerers and the Eight Immortals team up with each other and [[FutureBadass Good!Jade]] to stop [[FutureMeScaresMe Evil!Jade]] from releasing it.]]
** Jade and Raven teaming up against the Master of Games.
* ''FanFic/TheEquestrianWindMage'':
** The denizens of [[VideoGame/StoryOfTheBlanks Sunnytown]] -- minus Grey Hoof and the Bone Fiends, who are [[VillainTeamUp working with Ganondorf]] -- ally with the Mane Six and Vaati in order to retrieve the Element of Honesty.
** The fact that Ganon is oppressing ''everyone'' in Equestria leads to alliances with the Diamond Dogs and Changelings against him.
** In Season 3, the above alliances are still in effect, and with the monsters reformed, this will undoubtedly happen as contact between Equestria and Hyrule is made in the wake of [[BigBad Majora's]] attack.
* ''Fanfic/TheBridge'': Monster X and the Sirens are forced to team up when Enjin shows up and tries to kill them all.
* ''Fanfic/{{Wonderful}}'': [[ButtMonkey L33t]] went so mad when he realized that [[TheEngineer Squealer]] stole his tech and made it work that he and his partner-in-crime Uber fed information to the heroes to help them to beat up Squealer's gang.
* ''FanFic/SonOfTheSevenKingdoms'':
** [[FriendlyNeighborhoodVampire Serana]] aids the [[VampireHunter Dawnguard]] in fighting other vampires.
** When the Mythic Dawn opens an [[HellGate Oblivion Gate]] during the Battle of King's Landing, William's Legions and the Lannister-Tyrell alliance quickly call a ceasefire and work together to stop the monsters emerging from it.
* ''Fanfic/OutOfTheCornerOfTheEye'':
** [[ArchEnemy Shendu]] allies with Jackie and the others against the Outer Gods/Old Ones. As he puts it, he gets revenge for [[MindRape what was done]] to [[EvenEvilHasLovedOnes his son]], and eliminates potential competition, while the Chans get to protect their world, so everyone wins.
** The Chans and Section 13 fight alongside Po Kong against the Shoggoth. [[spoiler: Po Kong betrays them by trying to steal the Shoggoth's power, but gets exorcised for her troubles.]]
* ''Fanfic/ViolenceInTheLibrary'': [[Franchise/StarWars Post-Bespin]], [[VillainousRescue Darth Vader saves Luke Skywalker]] from [[Franchise/{{Alien}} the Xenomorphs]], and the two team up to destroy them.
* ''[[Fanfic/GuardiansWizardsAndKungFuFighters Guardians, Wizards, and Kung-Fu Fighters]]'':
** After the Sack of Torus Filney exposes the [[HeWhoFightsMonsters dark side of the Rebellion]], Will convinces Caleb and the other disgusted members of the leadership to seek a less violent path to victory by allying with members of Meridian's nobility who are opposed to Phobos' tyranny, in order to ease their campaigns going forward.
** [[HumanoidAbomination The Tracker]] and [[spoiler:[[MysteriousWatcher Nimue]]]] both have vastly different goals, but are willing to work together to destroy the Oni.

[[AC: ''Manga/DeathNote'']]
* In the CrackFic ''Fanfic/AllYouNeedIsLove'' Light seeks help from L and Naomi Misora after [[HilarityEnsues "misplacing" a Death Note.]]
* In ''FanFic/ACureForLove'' [[ArchEnemy Light/Kira considers L]] to be his "partner" in destroying the [[WesternTerrorists Astraea Organization]] [[spoiler: [[HijackedByGanon at first, before he usurps control of their organization]]]].

[[AC: ''Series/DoctorWho'']]
* In [[https://www.fanfiction.net/s/10568721/1/Survival-of-a-Monster "Survival of a Monster"]] the 11th Doctor, Norine and a Rutan form an alliance to stop King Wurzin and the Tufgup learning space travel with a Rutan ship.
** From the same author, "Game of Doctors" has a lot of this as the 7th Doctor in the [[https://www.fanfiction.net/s/9868669/8/Game-of-Doctors 8th chapter]] is forced to make an alliance with Callidus Dominus and the Malphan Empire to defeat the Virmok Empire. Later with the help of the 11th Doctor he gets the Daleks to attack [[spoiler:the Master's Cyberman world]] in the [[https://www.fanfiction.net/s/9868669/16/Game-of-Doctors 16th chapter]], which makes the 9th Doctor furious.

[[AC: ''Series/DragonBall'']]
* The plot of [[https://www.fanfiction.net/s/11767392/1/Frigid-Future Frigid Future]] is this. Cooler tries to avenge Frieza's death, only to find Goku and the other Z Fighters have been killed by the androids. Thus, Cooler must from an alliance with the forces of Earth to get his revenge.

[[AC: ''WesternAnimation/FairlyOddparents'']]
* In ''FanFic/NeverHadAFriendLikeMe'', the [[LawfulEvil Pixies]] and the [[ChaoticEvil Anti-Fairies]] have mutually exclusive goals for the world. They have, however, teamed up together temporarily in order to remove an obstacle to both their plans: Timmy Turner.
** [[spoiler: Later, they join Norm, Timmy, and his fairies in trapping [[EldritchAbomination Bob]] in another dimension]].

[[AC: ''Franchise/{{Halo}}'']]
* ''FanFic/EnemyOfMyEnemy'': ExactlyWhatItSaysOnTheTin, and awesome. Take a UNSC colony and add one shipload of Elites being chased by one carrier full of Brutes...

[[AC: ''Literature/HarryPotter'']]
* In ''FanFic/{{Sluagh}}'', apparently a Wizard BigBad is exactly what's needed to get the Real IRA and the Unionist militia to work together.
* Most stories focusing on Slytherin (particularly Slytherin!Harry) will give the House a simple rule that any problems with housemates stays inside the House. Against the other three Houses, they show a united front regardless of their feelings towards one another.
* ''FanFic/ASnakeNamedVoldemort'' has this between Voldemort and Harry, initially at least.
* In ''[[https://www.fanfiction.net/s/12031399/16/A-Year-Too-Soon A Year Too Soon]]'', basically every Slytherin takes Harry's side over Draco's. While several don't like Harry despite him being one of them, but they acknowledge that he does his best to help the house while Draco is a spoiled brat who thinks throwing his father's name around will get him anything he wants.
** Pansy's family announces their willingness to help Hermione press charges after she's injured by the Troll because whoever did it once could do so again, and Pansy's father [[PapaWolf will do anything to protect his little girl]].

[[AC: ''WesternAnimation/InvaderZim'']]
* ''FanFic/MyHostageNotYours'': Zim originally helping out Gaz (and Dib by extension) is this trope, before [[RelationshipUpgrade evolving]].
** Tak teams up with Dib's [[LaResistance Group]] in the third story just for revenge against Zim. [[spoiler: When they defect from the Swollen Eyeballs, they team up with Zim and Gaz to defeat them.]]
* ''Fanfic/TheNewAdventuresOfInvaderZim'':
** In Episode 3, Dib and Tak team up to fight off [[OurVampiresAreDifferent Norlock]] when he shows up to kill her, with Dib deciding Tak is the LesserOfTwoEvils. However, Tak makes it clear that they are ''not'' FireForgedFriends because of it.
** In Episode 11, when Zim's latest experiment (genetically engineered plant monsters) turn on him, he has to ally with Dib's Team Save Earth to destroy them. [[spoiler: Tak shows up partway through the fight to aid them, just because she sees the plants as a threat too.]]
** In Episode 13, Zim and Skoodge team up with Tak to rescue Tenn from [[FunWithAcronyms CREAM]]. Lampshaded by Tak quoting the TropeNamer, when Norlock points out that they don't have to like each other to get it done.
** In [[BeachEpisode Episode 15]], we see Dib, Zim, and Tak's groups all reluctantly teaming up to fight the sea hydra that attacks them.

[[AC: ''WesternAnimation/JackieChanAdventures'']]
* ''FanFic/QueenOfAllOni'': When Valmont uses the power of Kaito's mask to steal the Ninja tribe away from Jade, she and Jackie briefly (and reluctantly, in her case) team up to defeat him.
** Subverted in one of the scenes set in [[GhostInTheMachine Jade's mindscape]] -- Hero tries to form an alliance against [[SuperpoweredEvilSide The Queen]] with his apparent rival Father, but is rejected.
** In a similar subversion, the J-Team refuses to ally with [[FutureBadass Karasu]] against Drago, as they don't see any good coming from working with a Shadowkhan.
* ''Fanfic/TheUltimateEvil'': After Jade's trapped in the Netherworld, Valerie goes to bargain the Pan'Ku Box from Shendu, resulting in the J-Team having to travel with the Demon Sorcerer and Hak Foo to the Fire Demon's portal so that Shendu can use the [[WonderTwinPowers power boost provided by his Other]] Valerie to keep the portal open long enough for Jade to escape. [[spoiler:Shendu's then banished before any of his siblings can escape as well.]]
** When [[spoiler:the damaging of the Book of Ages creates an all-consuming vortex]] during the climax, Shendu sets aside the animosities with the heroes in order to [[spoiler:bring Valerie to the Book so that she can fix it]].
** In the sequel, ''The Stronger Evil'', Drago ends up accidentally releasing Tarakudo from his [[SealedEvilInACan imprisonment]] and has to team up with the J-Team to put him back down. Eventually Valerie proposes a full team-up with Drago and Shendu, with [[spoiler:only [[HunterOfMonsters Nataline]] of all the members of the J-Team agreeing to it at all]].
* ''FanFic/{{Webwork}}'': The Mexican crime boss known as the Old Colonel convinces the J-Team to protect him from the Oni Essence-empowered Chang and help take him down, by pointing out that [[LesserOfTwoEvils it's better than]] letting Chang kill him, take over his assets, and go to ground with it all. [[spoiler: They do help, but set the Colonel to be arrested by the Mexican police.]]

[[AC: ''WesternAnimation/MyLittlePonyFriendshipIsMagic'']]
* ''FanFic/ABriefHistoryOfEquestria'': When Wind Whistler led a coup against [[TheCaligula Commander Sullamander]], she recruited help from Star-Swirl the Bearded and the few unicorns loyal to him. True, Star-Swirl was open-minded and friendly with the other tribes, but that's still members of one nation asking help from members of a rival nation to overthrow their leader.
* ''FanFic/TheImmortalGame'': In a plan [[GodzillaThreshold born of desperation]] to defeat [[BigBad Titan]] during the FinalBattle, the Mane Six end up allying with [[spoiler: Discord]]. As [[spoiler: Celestia]] puts it, they know the latter will probably betray them after they're done with Titan, but they can handle that, and besides, "[[LesserOfTwoEvils better the devil you know]]".
* ''FanFic/ThePowersOfHarmony'': After she [[spoiler: [[DemonicPossession possesses her]]]], [[TheDragon Eclipse]] is able to convince Rarity to help her [[TheStarscream plot against]] [[BigBad Cetus]], and together they plan to bring Twilight into the fold as well. Or at least, [[GuileHero that's what Rarity wants Eclipse to think]].
** Played straight when the Changeling Princess Pupa allies with Applejack's group to stop (her sister) Chrysalis' invasion of Gildesdale, with the promise that afterwards she'll also ally her people with the ponies against Cetus.
* At the climax of ''[[FanFic/PoniesOfOlympus Rolling in Beaches]]'', Spike convinces the hippocampi and Scaly Back River Clan dragons to put aside their differences in order to stop all the dragons [[spoiler: and Mane Six]] turned into monsters by [[TheCorruption the Rainbow of Darkness]].
* In the ''FanFic/PonyPOVSeries'', the backstory for the [[BadFuture Dark World]] has this happening twice between [[EvilOverlord Discord]] and the various LaResistance groups arrayed against him (primarily the [[HeelRaceTurn Changelings]]) -- first during the [[AlienInvasion invasion]] by the [[TabletopGame/{{Warhammer40000}} Imperium of Man]], then centuries later during his [[EvilVersusEvil war with Grogar]] (in both cases, Discord was viewed as the LesserOfTwoEvils).
** Clover's story in the ''7 Dreams/Nightmares'' collection reveals that eons ago, a group of {{Eldritch Abomination}}s escaped the loss of their own reality by entering the POV [[TheMultiverse multiverse]] with the intention of absorbing all beings into their HiveMind in order to torment them for all eternity. This offended ''both'' [[TopGod Fauna Luster and Entropy]] -- the former because She's a strong believer in free will, and the latter because it would potentially prevent the end of all things She [[OmnicidalManiac embodies and desires]] -- leading to Them, Their Mates, and Their respective children working together to defeat these things and [[SealedEvilInACan seal them]] beyond the Gates of Tartarus. It's noted in-universe that this is the ''only'' time the two of Them have ''ever'' agreed on ''anything''.
** During the Wedding Arc, while they're unaware of it, the heroes' efforts are being aided from the sidelines by [[spoiler: Discord and Nightmare Diamond]], who are aware that if Chrysalis succeeds in her plans, she'll be [[AGodAmI powerful enough]] to be a threat even to them.
** During the Finale Arc, [[spoiler: when Discord and his allies begin their [[RewritingReality endgame plan]], it's so horrifying that a group of alternate dimension [[SuperPoweredEvilSide Nightmares]] show up to help stop them]].
* In ''FanFic/TheConversionBureauColdWar'' the United States of America and the Soviet Union put aside all differences to fight a xenocidal race of Ponies.
* ''FanFic/EscapeFromTheMoon'': [[spoiler:After the peace treaty between the "Pures" and the group rebelling against them was signed, Spliced Genome continued to create the plagues she'd used against the Pures on behalf of the rebels. Both sides promptly teamed up to capture her and lock her up.]]

[[AC: ''Manga/{{Naruto}}'']]
* ''[[http://www.fanfiction.net/s/6585953/1/Boutoku-no-Naruto Boutoku no Naruto]]'' has Kyuubi willing to help Naruto out of hatred for the shinigami. When [[ForWantOfANail Naruto learned Edo Tensai instead of Kage Bunshin]], Kyuubi offered him a deal.
-->'''Kyuubi''': "Because I hate. There are many things I hate. The Sage of the Six Paths. Madara Uchiha. Hashirama Senju. Mito Uzumaki. Minato Namikaze. The toads. Kushina Uzumaki. But more than anything else, I hate the Shinigami. He stole over two thirds of my power, and claimed the Namikize's soul in return, a violation of his own laws and rights. The Shiki Fuin, the contract with the Shinigami, works on a simple basis. A soul for a soul. He did not take my soul, merely my power. When I was sealed, he had nothing to do with it. By the ancient laws, he should have let the Namikaze go, or at least send him to the Pure World, and return my power to me. But he didn't, breaking ancient law. ... You see, he has stolen from me, so I will ensure that he suffers for it! You Naruto, are the key of my vengeance. Through you I will make him suffer. All I ask is that you call back many, many souls, I don't even care for what, and in return, I will give you what all other jinchuuriki can only dream of, my full support."
* In ''[[http://ficwad.com/story/242784 Eroninja]]'', Danzou and Joseki work together to destroy the Suna/Konoha alliance, viewing it as weakening their villages in the long run. Also, if they can instigate a war between the two, they'll have a chance to try and kill each other for their actions in previous wars.
* Several stories, such as ''[[http://naruto.adult-fanfiction.org/story.php?no=600105912&chapter=6 Genjutsu Gone Right]]'', explain that the point of D-Rank missions is primarily to unite a genin team... against their teacher for making them do glorified chores.

* ''Fanfic/AdviceAndTrust'': Shinji's female classmates have a crush on him and team up to keep Asuka away him as each one of them try to ask him out. However Rei does not care for them trying to flirt with Shinji so that Rei teams up with Asuka to keep them away Shinji (and in the process they become [[TrueCompanions good friends]]).
* ''Fanfic/{{HERZ}}'': The US Government and SEELE does not like or trust each other, but they join to destroy secret organization GEIST. On the other hand, GEIST lends its support to NERV's successor HERZ to take down SEELE.
* ''Fanfic/OnceMoreWithFeeling'': Neither Gendo nor SEELE can stand each other but they're working together until all Angels are defeated.
-->Their investigations had uncovered that there was some kind of friction between SEELE and their point man at Central. As far as Kaji had understood and explained it, the goals of SEELE and Gendo meshed well until some undetermined point in the future, at which point… things would probably happen.\\
Both sides ''pretended'' it wasn't the case, but both sides ''knew'' the truth and were constantly maneuvering for position even as they worked together closely on what they needed to cooperate on.

[[AC: RealPersonFic]]
* Villain example: Although [[spoiler: Brox and Co.]] and the Raleka in ''Fanfic/WithStringsAttached'' aren't exactly mortal enemies, they dislike each other considerably. [[spoiler: Brox and Co.]] are contemptuous of Ketafans in general, and the Raleka hate that the skahs want to use the sacred Vasyn for stupid purposes. However, they work together against the four because the Raleka cannot do certain things without [[spoiler: Brox's help]]. We find out later that [[spoiler: Brox and Co.]] were planning to betray the Raleka, but Paul and George inadvertently screwed this up for them.

[[AC: ''Franchise/SpiderMan'']]
* One issue of ''[[FanFic/UltimateSpiderWoman Ultimate Spider-Woman: Change With the Light]]'' has petty criminal Blizzard teaming up with Spider-Woman to help her protect the innocent people in danger during an invasion of New York City by an army of BrainwashedAndCrazy super villains. Taking inspiration from the ''WesternAnimation/DarkwingDuck'' episode where DW teamed up with Megavolt (see below), Blizzard points out that if New York is destroyed, there'll be nothing left for him to rob.

[[AC: ''Franchise/StarTrek'']]
* "Fanfic/FlaihhsamSSpahkh": Spock casts the Romulans giving the Federation a cloaking device for the USS ''Defiant'' as an alliance against a poorly understood enemy (the Dominion). [[DoomedByCanon The alliance had collapsed by the time the Dominion War broke out.]]
* ''Fanfic/PeaceForgedInFire'': Praetor Velal of the Romulan Star Empire becomes disgusted at the underhanded attempts of the Tal'Shiar to disrupt the peace talks between the Empire and the Romulan Republic, and joins with his opposite numbers to take them down. During the talks they also prepare command protocols for joint military operations against enemies like the Undine and Borg.
* ''Fanfic/RealityIsFluid'': Eleya is able to convince an Undine commander that the Federation et al. were ''not'' responsible for the attacks on Undine spawning pools and hatchlings that sparked the current war, and that faction begins targeting the Undine that have been infiltrating the Alpha and Beta Quadrant powers ''and'' agrees to join the fight against the [[BigBad Iconians]] when the time comes. [[spoiler:This pays off in the later story ''Fanfic/BeatTheDrumsOfWar''.]]
* In the fic ''[[https://www.fanfiction.net/s/9694363/1/Safe-and-Sound Safe and Sound]]'', Kirk and Khan pull one of these, similar to the one they pulled in the [[Film/StarTrekIntoDarkness second film]], in order to save the [[spoiler: kidnapped Nyota Uhura, Joanna [=McCoy=] and Lucille Harewood. This time, Khan doesn't betray him]].
* In ''Fanfic/TheWrongReflection'', Eleya allies with the Klingon-Cardassian Alliance to attack a Terran Empire installation, but Eleya worries that the Alliance may turn on her to get its hands on the USS ''Bajor'''s technology.
* In "Fanfic/PastContinuous", as in canon the Federation and the Klingons are technically still at war throughout the 2800 incident (though active hostilities have died down), but they're working together to eject Loriss from Deep Space 9. Eleya remarks to Kagran that after the Jem'Hadar are dealt with "we can go back to hating each other, but until then, I want your word you'll keep [[http://sto.gamepedia.com/K'men K'men's]] people in line."

[[AC: ''VideoGame/StarWarsTheOldRepublic'']]
* ''Fanfic/BloodAndHonor'': Sith Lord Sanguis and her team join forces with Republic soldiers on one occasion, Organa troops on anther, and a Jedi Master on a third. The first two team-ups are more or less voluntary - trading a favor for a favor - but the Jedi Master blackmails Sanguis into the alliance and she's ''not'' happy about it.

[[AC: ''Franchise/TolkiensLegendarium'']]
* In ''FanFic/AFarGreenCountry'', Durus and Surad were enemies of Elden and Nellas, but these four quickly become allies when they are chasing a common enemy.

[[AC: ''Franchise/{{Transformers}}'']]
* In ''Fanfic/AChildShallLeadThem'', the Dinobots end up teaming up with Galvatron and Cyclonus to escape the Quintessons. Galvatron ends this alliance fairly quickly when he literally stabs Pterodactus Prime (aka Swoop) in the back.

[[AC: ''TabletopGame/{{Warhammer 40000}}'']]
* ''FanFic/RiseOfTheTau'' has TheRemnant of the Imperium, the [[AlwaysChaoticEvil Forces of Chaos]], [[BloodKnight da Orks]], [[OurElvesAreBetter the Eldar]] and [[spoiler:[[MySpeciesDothProtestTooMuch Farsight's Tau rebels]]]] teaming up against the Tau Empire. [[spoiler:Also, the Chaos Gods, Gork and Mork, Ynnead and [[AscendToAHigherPlaneOfExistence the Emperor]] tearing apart the Deceiver]].

[[AC: ''Literature/{{Worldwar}}'']]
* ''FanFic/WorldwarWarOfEquals'': In light of the pending threat of invasion by the Race, various nations around the world put aside their differences to form mutual defense pacts:
** Egypt and Israel set aside differences and set up a military alliance with Turkey before The Race arrives.
** Colombia and Venezuela, who were waging a war just months before the Race's arrival, agree to a cease fire and start preparing for the incoming invasion.
** Every drug cartel in Ciudad Juarez fights alongside the Mexican military in the city against Race forces.

[[AC: ''Literature/{{Worm}}'']]
* In FanFic/{{Cenotaph}} Purity and [[GuileHero Skitter]] team up to fight the ABB. On one hand a flying Blaster, [[TheAtoner ex-Nazi]] single mother. On the other, a ruthlessly intelligent, highly resourcefull teenage highschool student and [[spoiler: newly-minted orphan]] with dreams of being a hero. Together, they fight crime!

[[AC: ''Wrestling/{{WWE}}'']]
* In ''The Return-Remixed'', the remaining WWE Divas slowly come together, make peace with each other and unite to fight the bigger threat, the super-stable of returning Divas, DEAR. Wrestling/MichelleMcCool even says "the enemy of our enemy is our friend" when burying the hatchet with Wrestling/{{Natalya}}.
[[AC: ''Series/TheXFiles'']]
* The example from WildMassGuessing for ''WMG/TheXFiles'', suggesting that as soon as the aliens arrive on Earth, they'll promptly be beaten back by ''every single MonsterOfTheWeek'', who tend to favor continuing to live on their planet.
[[AC: ''Franchise/YuGiOh'']]
* In ''FanFic/{{Glass}}'', Kaiba plans to work with everyone, even those he personally dislikes, in order to escape. Yami Bakura and Joey feel likewise.
* ''Fanfic/ShadowchasersConspiracy'' has Italian mobster Fanciullo Cattivo forming a reluctant partnership with the heroes for mutual protection; both sides have emphasized it's temporary nature.