Characters, hostile to each other, indifferent, or strangers, must fight on the same side. All the way up to an Enemy Mine situation. Afterwards, they are no longer hostile and perhaps even actual friends. If they continue as enemies, they are Friendly Enemy.
Bonus points if:
After being forced to team up, Ichigo Kurosaki and Uryu Ishida quickly became best friends...though Uryu refuses to admit it. He tries to insist that Ichigo is still his sworn enemy, except that his actions (and even his words) prove he's full of it.
In a flashback, Ichigo and Chad seem to be this to a degree. Ichigo was initially hostile towards Chad (questioning his Technical Pacifism and passively accusing him of lying) but turned up to save him when he was attacked (and of course refused to defend himself).
Negi and Kotaro go through this in Mahou Sensei Negima!; they start out as enemies, have to join forces to defeat a demon, and are good friends after that.
Ditto Yue and Emily Sevensheep: Emily starts off as the Alpha Bitch, but opens up to Yue after Yue saves her from a Griffin Dragon.
One Piece: Pretty much the formula for adding onto Luffy's True Companions. He makes an offer, which they usually refuse at first. He then fights the current Big Bad by their side and afterward they usually make the decision to join his crew. Zoro, Nami, Sanji, Chopper, and Brook all joined this way, while Usopp was invited after the Big Bad was defeated and did not hesitate, and Robin invited herself.
Franky may be the best example of this among the Straw Hats. Initially, the dislike was mutual; Luffy (and the rest of his crew) hated Franky for beating up Usopp, and Franky wanted revenge on Luffy for blowing up the Franky House and beating up his Family (in retaliation). The two put aside their differences when CP9 came into the picture, and Franky's reluctance to join the crew after the whole thing was over was mainly due to having attachments to Water 7 and his Family.
Surprisingly, Gold Roger invokes the trope as he speaks to Vice-Admiral Garp right before he's executed. He says that they are as good as friends given how long they've known each other, and on this principle trusts Garp to protect his soon to be born child from the Marines. Despite the other person's initial disbelief, it works.
A pair of slightly lesser examples are Smoker and his protégé Tashigi of the Marines. They pursued the Straw Hats to the Grand Line after they escaped Loguetown, and didn't think of them any differently than other pirates (aside from considering them more threatening than most). Then comes the Alabasta arc, where the Big Bad, Crocodile, imprisons some of the Straw Hats and Smoker in a cage and explains his Evil Plan to them. Smoker shows the first sign of this trope when they escape, he only escaping with his life because Luffy had him saved, by letting the Straw Hats go free, though it would be fair to say that that's because of his Lawful Good nature. After that, Smoker passes command to Tashigi while he informs his superiors, and she allies with the Straw Hats in order to bring Crocodile down. At the end of it all, Smoker and Tashigi still hold a grudge against the Straw Hats as pirates, but they respect them a lot more.
Then, after the Time Skip, we have the Punk Hazard Arc. Vice-Admiral Smoker and Captain Tashigi, now the commanders of a base filled with Ax-Crazy Marines, are waiting to intercept the Straw Hats in the New World, but when they take an unexpected detour to an island that is supposed to be deserted, they head there. They soon find out that something very fishy is going on, and are caught in the middle of it, undergoing a "Freaky Friday" Flip as one of the first fragments of trouble. Eventually, both of them end up trapped in a cage with the Straw Hatsagain, (and Robin, who was The Dragon when it happened last time, lampshades it) along with the Big Bad's subordinate Shichibukai Trafalgar Law who had revealed himself to be a Wild Card, and watching the Evil Plan play out in front of them. When they escape, the Marines are forced into a full-blown Enemy Mine with the Straw Hats and Law, including such things as Sanji taking command of the Marine underlings and Tashigi and Zoro teaming up against The Dragon. At the end of it all, Smoker and Tashigi seem to be almost friendly with the Straw Hats, while their subordinates flat-out state that they admire them.
Initially, Team 7 starts out as a jumbled mess of dysfunctional relationships: Naruto hates Sasuke, Sasuke finds Naruto and Sakura annoying, Sakura has a crush on Sasuke, Naruto has a crush on Sakura, but Sakura can't stand him. Once Kakashi puts them into a situation where they're forced to work together, they start to get along and become friends. However, Sasuke pulls a Face-Heel Turn at the end of Part 1.
At times, even the bitter relationship between Naruto and the Kyuubi is like this. When Naruto is on the brink of death, the Kyuubi would willingly lend chakra to him to protect himself. However, during the War, when the real Madara appeared and attempted to summon the Kyuubi, he gave as much chakra as he could to Naruto, saying that he would rather help Naruto than be controlled by Madara.
During the time between A's and StrikerS, Vita became much less distant to Nanoha after she failied to protect her in the mission involving the Type IV Gadget Drones who nearly killed Nanoha.
Similarly, Nanoha and Arf in Season 1; Arf initially dislikes Nanoha, thinking of her as far weaker than Fate and being suspicious of her motives for reaching out to Fate. After Arf gets thrown out of the Garden of Time, she reluctantly decides to accept Nanoha's help in saving Fate. By the time Nanoha becomes friends with Fate, Arf has also come to like her.
In YuYu Hakusho, Kuwabara goes from being an Unknown Rival to Yuusuke to being his best friend this way after they find themselves on the same side by coincidence more than once.
This is a recurring trope in Studio Ghibli works due to the rarity of actually evil antagonists:
In Ranma ˝, this is Ranma and Ryoga's friendship to the core. Ryoga may have spent half his life obsessed with exacting vengeance against Ranma, and Ranma may hate the whole P-chan situation, but by the end of the series they've had so many Enemy Mine team-ups that they're probably the most trustworthy ally either one has. After Mousse joins them to help defeat Prince Herb, he too falls under this category.
Suzumiya Haruhi: Sure, Mikuru, Itsuki and Yuki may have competing objectives and ideals, but when Kyon tells them that, for example, he needs Yuki and Mikuru to help him fix an alternate universe, they will move mountains to achieve the goals. This has reached the point where the three of them have sworn allegiance with the SOS Brigade, and are willing to go against their vastly more powerful superiors if they end up with a conflict.
Pokémon Special give us Gold and Silver. They first meet after Silver steals one of Prof. Elm's Pokemon, and Gold sets out to beat Silver and retrieve said Pokemon. They meet up a few more times, and Silver tells Gold to stay out of his way each time. They don't start to act like friends until the Lake of Rage, when Gold finds out Silver's backstory, Silver sees Gold stand up for him, and they realize they have a common enemy in The Mask of Ice. At the end of the saga, Gold sacrifices himself to so that Silver (and Crys) won't have to, and Silver almost cries because of it. Gold gets better.
Persona 4deconstructs this trope. The Protagonist Yu is forced to live out his nightmare in which the murders stop in his town. With no more murders, all of his friends drift apart, because the only thing keeping them together was solving the murders, and without them, they had nothing in common. In the end, it was just that, a nightmare. In reality, they had already developed into True Companions.
Higurashi Reishows that, if the tragedies in everyone's life never happened, they wouldn't be friends. On top of that, Satoko, Rika's closest friend of the group, would be bullying her and Keiichi wouldn't even be in Hinamizawa.
In Mai-HiME, Natsuki and Mai initially dislike each other, but by the end of the series, consider each other close friends.
In Thunderbolts, when they were sent after Spider-Man, MACH-1 was delighted with the prospect of bringing down his old enemy, even suggesting at one point they could kill him and claim it was an accident. After they fight as Back-to-Back Badasses against the rest of the Thunderbolts under mindcontrol, and Spider-Man saves his life, MACH-1 gives him the evidence he needs to clear his name, because he couldn't betray him after fighting next to him like that. (Also, realizing that he was Becoming the Mask.)
Dick Grayson (the first Robin) had this with Jason Todd (the second Robin). Dick resented Jason for taking his place, and Jason didn't like Dick for assuming he knew better than Jason did (which, after all, he did). After an evening together saving Alfred's life, they got close enough that Dick offered to be there when Bruce inevitably turned dickish again.
Hulk and his Warbound became friends after experiencing great challenges together as gladiators, and their first moments of cohesion are in the volcanic gladiator training camp, thus being almost literally fire forged. Newer members of the Warbound (such as Caiera and Kate) join the Warbound after similar trying circumstances. In-universe, the term "Warbound" explicitly invokes this trope, having fought side-by-side they have bonded and become bound together.
In an issue of X-Factor, Scott smashed up the house where he had lived with Madelyne, and found the baby's rattle. A cop finds him in the ruins and is belligerent, addressing him as "mister", threatening arrest. A Sentinel attacks, and they must join forces against it. After its defeat, Scott speaks of the arrest, and the cop says "son", he didn't remember it like that at all; the Sentinel had smashed up the house.
In an issue of X-Men, Wolverine was enraged by Rogue joining the team. After the rest of the team was taken out by poison, they go after the enemies responsible together. It culminates in Rogue taking an attack meant for Wolverine and Mariko — and Wolverine forcing her to absorb his healing factor to save her life despite his own injuries.
Although most other adaptations like to play up their conflicts, Cyclops and Wolverine actually develop a begrudging respect for one another in the comics.
Wolverine and Angel have also become this after stubbornly hating each others guts for several decades.
In Punisher: War Journal, Frank and the Rhino make peace as they face Alyosha Kravinoff, the new Kraven, in his sadistic game of hunting supervillains with animal motifs. Over the course of the incident, it's revealed that the murder that set Frank on the Rhino's tail was an accident (and that Rhino sends money to the man's widow), and when Frank saves Rhino's life they decide to call it even. They then develop a Sam the Sheepdog/Ralph the Wolf sort of relationship, except they've cut out the "antagonize one another" part entirely.
Played with in Anti-Venom between Eddie Brock and Frank Castle: after taking down a drug lord together, Eddie Brock thinks they've got this when Frank Castle appears to let him live. Frank Castle, on the other hand, knows he just ran out of bullets.
Victor Von Piro and the Frank's gang in Mini Monsters. At first, Victor doesn't get along with them and the Frank's gang dislike him completely (Except Piruja who is obsessively in love with him). However, Frank only admitted him because he was so socially awkward that he would not make friends of his own. However, despite his strong dislike for them, he prefers being with them than his biological family (A very embarrasing one).
Piruja can also count, but she's liked a lot more than Victor, as she's accepted when she's not in her Abhorrent Admirer mode.
In H'el on Earth, when Superboy meets Superman for the first time, he's untrusting of him; only teaming up with Superman because he saved his life. Over time, Superboy warms up to him, impressed by how well he handles situations. He even offers to call in his friends, the Teen Titans to help battle H'el.
When Xavin first showed up, he/she was not particularly well-liked by the Runaways, who suspected that he/she was just taking advantage of Karolina's low self-esteem, and who found his/her arrogance annoying. However, Xavin earned his/her place on the team after risking his/her life to distract the Gibborim while the rest of the team tried to talk Chase out making a deal with them to restore Gert to life.
Molly Hayes: I don't care what shape you are... you're totally my sister now.
Cenotaph features the Skitter and the Undersiders. Not as close as in canon yet, but still on good terms, and friendly... And also Purity, who joined up while Taylor was fighting the ABB. Both helped each other, Taylor giveing Purity hope that her attempts to clean up Brockton Bay would bear fruit, and Purity giving Skitter an ally in a time when she felt very alone.
Remaining consistent with the original series, A:TLAR's Team Avatar never leaves a member behind, (except for that one time...) and every one of them will fight and die alongside the others, proud to have known such great warriors. However, they can be considered closer to Fire-Forged Friends than the original, due to the general hostilities between members. As time goes by, they will surpass numerous conflicts, including Katara and Aang's feud, Sokka and Suki's brief falling out, and Zuko and Iroh's temporary split from the team during Books Two and Three.
Blind: While already on good terms, 3 years as missing-nin turns Naruto and Gaara as this.
In Tangled, the Bar Brawl and escaping down the tunnel together gets Flynn friendly enough to ask why she didn't go before; The Chase, culminating in their nearly drowning, and their final escape, cements it so that Flynn no longer sulks over guiding her, and they confide in each other.
Monsters University, Mike and Sully finally become true friends after their competitive rivalry when the two have to escape a human summer camp by teaming up to scare a group of adults to power the door from their side.
Films — Live-Action
There is a humorous interplay in the second installment of Pirates of the Caribbean between Pintel, Ragetti, and Elizabeth Swann as they fight off Davey Jones' crew together. Swann's original relation to the plucky duo involved being captured and threatened throughout the first film.
Dan and Occam in The Patriot: Dan constantly talks smack about former slave Occam, right up until the latter runs back to rescue the former in the heat of battle. From then on, Dan is honored to have Occam at his side.
In the Dawn of the Dead (2004) remake, the security guards at the mall are initially hostile towards the new arrivals, but eventually their common purpose against the zombies makes them allies. Not all of the survivors manage to work together, though, and indeed this trope is rare in the zombie movies made by or remade from George Romero. Usually the conflicts between survivors escalate to become their undoing.
Gandalf and Pippin come to mind. While the Fellowship were True Companions, Gandalf never seemed to like Pippin very much. Once they had fought together in Minas Tirith, lived through the siege and saved Faramir's life, Pippin seemed to have become Gandalf's favorite among the Fellowship members (especially in the movie).
Also, Gimli and Legolas:
Gimli: I never thought I'd die fighting side-by-side with an Elf!
District 9: Wikus van de Merwe and Christopher Johnson.
Done in the Clash of the Titans remake. The Argos captain almost shoves Perseus's head into flames before the king calls him off, allows the monster hunters to come along as meatshields, and doesn't trust the Djinn even after they save the group. Perseus eventually comes to say he trusts the surviving men, woman Io, and whatever the hell the Djinn is.
Lethal Weapon: Riggs and Murtaugh don't particularly like each other when they first meet. But by the end of the film, Murtaugh is inviting Riggs to spend Christmas dinner with his family. And after a while, Riggs is family.
A famous example of this trope happens in A New Hope. When Luke Skywalker and Han Solo first meet they don't like each other at all, it is only after saving Leia together that their friendship begins.
When The Avengers first assemble, they don't get along at all. The main arc of the film is this motley collection of alpha dogs going from "we're six guys who all happen to want the same thing" to becoming the motherflippin' Avengers.
Special mention has to go to both Captain America and Iron Man. At first, the two really can't stand one another, with Cap even wanting to punch Tony's lights out at one point, but with the fate of the world at stake, they're more than happy to drop all grudges and get their act together to save humanity from Loki and the Chitauri.
Special mention also goes to Black Widow and the Hulk. At first, Bruce Banner is suspicious of Natasha and only reluctantly goes along with her, but as the story moves along, Natasha tries to calm him down and comfort him, and before Bruce turns into Hulk at one point, he stops for a moment and looks mournfully at Natasha as if to urge her to run. By the end, they—like the other Avengers—are Fire-Forged Friends.
Nonhuman examples: Godzilla, Rodan, Anguirus, and Mothra. A strange group, to be sure. But each of these four became fire forged friends in different films in the Showa Era. Actually, Godzilla, Rodan, and Mothra are pretty much Toho's Power Trio. Anguirus is something like Godzilla's sidekick. Godzilla and Anguirus are adversaries during the second Godzilla film, but somehow or other ended up as great friends from that point after. How Anguirus manages to forgive Godzilla for— in essence—killing him is unknown, but even the Trendmaster's toy line roster calls Anguirus one of Godzilla's staunchest allies, and most films in which they appear together as allies make it clear that if Rodan is Godzilla's Right Hand, Anguirus is the Left. Rodan and Mothra become fire forged friends with Godzilla when they team up to defeat King Ghidorah, and remain friends, or at least Friendly Rivals from that film forward.
Ah Jong and Inspector Li from The Killer, who went from being somewhat amicable adversaries to something akin to Blood Brothers when the two joined forces at the beach house to defend themselves and Jenny against the assassins after Ah Jong.
Jack the Giant Slayer: At their first meeting, Elmont is not impressed by this bumpkin Jack. After Jack rescues him and Isabelle from being cooked by a giant and they subsequently send another giant plummeting to his death, Elmont gives Jack a King's Guard badge, saying, "You've earned it."
Stu Miley starts out hating the titular character of Monkey Bone. Then they sneak into the Land of the Dead together to steal an Exit Pass, learn to rely on other, and Stu even admits that he's come to like him. Then it gets averted all to hell when Monkey Bone betrays him, steals his exit pass, and leaves Stu in limbo.
How the Animorphs became friends. Before the meeting with Elfangor, they weren't close - Marco and Jake were best friends, Cassie and Rachel were best friends, but Rachel and Jake weren't close cousins, Cassie and Jake only barely knew each other, and Rachel and Marco only knew of each other. Nobody knew or liked Tobias much, and, of course, they had never met Ax. But as Marco notes, after someone saves your life a couple times, you tend to cut them a little slack.
Roland Deschain's second ka-tet in The Dark Tower, very much so. Eddie comes close to murdering Roland in cold blood while in the throes of heroin withdrawal and Susannah, while controlled by her Detta Walker persona, tries to kill both of them in cold blood several times.
Mátyás Furstán becomes such a friend with Kelson, Morgan and Dhugal as a result of their success in foiling Mahael's coup d'etat and Teymuraz's attempt to murder Mátyás in King Kelson's Bride. The process may have begun years earlier when Nigel Haldane protected himself and Mátyás' nephew Liam from assassins in The King's Justice.
Also in King Kelson's Bride, the existing alliance between the Hort of Orsal and Gwynedd is strengthened, and the formerly tense relations between Tralia (the Orsal's principality) and Torenth moves in this direction. This is in reaction to both an assassination attempt against Kelson and Liam at the Orsal's summer palace of Horthánthy and the need to pool resources against the threat of an escaped Teymuraz. Létald says, "It seems we must all trust one another far more than we had planned or dreamed."
"Brittney had no romantic feelings for Edilio, but what she had went a lot deeper. She would rather burn for eternity in the hottest fires of hell than let Edilio down. "
Dekka and Sam:
Sam: "I don't want to sound weird, but you know I love you, right?"
Dekka: " Love you too, Sam."
Diana has become this with Astrid and Sam at the end of Light.
Harry Potter: Harry and Ron's friendship with Hermione stems from a fight with a troll.
There are some things you can't go through together without coming out friends, and knocking out a twelve-foot mountain troll is one of them.
The battle in the Department of Mysteries in Order of the Phoenix pulls Luna, Neville and Ginny into the group, as well.
In Darkness Visible Lewis and Marsh don't become friends until after the disaster at Wandsworth Prison, the first time they save each other's lives (but not the last).
Temeraire: John Granby is initially extremely hostile to Laurence out of friendship to another officer who lost his chance at promotion because Temeraire wanted Laurence for a captain instead. But after being faced with Laurence's heroism and concern for his dragon in Temeraire's first combat action, Granby realizes he was being a Jerk Ass, apologises to Laurence, and becomes his friend.
Part of the main plot of Honored Enemy, of The Riftwar Cycle by Raymond E. Feist. During the war between Midkemia and the empire of Tsuranuanni, Dennis Hartraft and his company of Midkemian soldiers find themselves pitted against Asayaga, commander of a Tsurani platoon. The plot hook? Both companies find themselves in the territory of the vicious moredhel (dark elves), who are at war with both nations. These circumstances force the Midkemians and the Tsurani to work together to survive. Eventually, despite many fallings-out due to cultural differences and Dennis' pre-existing hatred of Tsurani for personal reasons, the two become loyal friends.
In Dan Abnett's Gaunt's Ghosts novels, while Rawne's hostility to Gaunt lasted through many battles, their work together in the Gereon resistance makes friends of them. (In His Last Command, Gaunt reflects on the strangeness of this.)
In Dan Abnett's Brothers of the Snake Antoni and Princeps become rather close after saving each others lives while accompanying Priad on a Dark Eldar hunt.
In Blood Pact, Kolea and Baskevyl talk, random chit-chat, in the lock-down when they can't act; they know it means nothing, it just expresses their friendship.
In William King's Space Wolf, after desiring Revenge the entire novel, Ragnar sees Strybjorn save his life, and then go down before a Chaos-tainted force. He realizes that he does not, and should not, desire revenge, which is petty in face of their common foes. When Strybjorn lives, Ragaor sends the others, over their objections, to Bring News Back, so that he can treat Strybjorn's injuries and bring him out.
In Graham McNeill's Storm of Iron, Captain Eshara speaks of how war brings out the best and the worst in men, and explains that the bond of brotherhood among the soldiers is not to be found in any other way.
In Graham McNeill's Ultramarines novel Dead Sky Black Sun, when Leonid saves the Lord of the Unfleshed from being attacked In the Back, the Lord salutes him as "Now you Tribe!" Minutes later, when the Lord saves his life, Leonid thanks him, and the Lord says, "You Tribe."
In Graham McNeill's Horus Heresy novel False Gods, the reunion of Torgaddon and Tarvitz makes their friendship from the heat of battle clear to everyone.
In Ben Counter's Horus Heresy novel Galaxy In Flames, when Tarvitz is trying to warn the betrayed Marines on Isstavan III, he invokes The Power of Friendship to get Garro to believe his word. It is their Fire Forged Friendship that wins him.
As my honor brother I ask you to trust me like you have never trusted me before. On my life I swear that I do not lie to you, Nathaniel.
Later in the same book, Tarvitz tries to join the Emperor's Children partly so he will die with his brothers in defiance of the treachery that separated them from other battle brothers. In the end, he realizes that he knows the names of all the men who are dying with him, even those who were not in his legion. In the face of certain death, he consoles them with the thought that they hurt Horus.
In Matt Farrer's "After Desh'ea" (in Tales of the Heresy), Angron laments his dead comrades from the Gladiator Revolt; his War Hounds/World Eaters crave it from him so desperately that Kharn feels envy listening to his account.
In Sandy Mitchell's first Ciaphas Cain (HERO OF THE IMPERIUM) novel For the Emperor, the Valhallan 296th/301st is an amalgamation of two regiments that were both depleted by a Tyranid attack... and each regiment collectively hates the other one. One of the first things the titular commissar has to do when he's reassigned there is put down a riot between the two factions through sheer force of will. Afterward, however, thanks to both reforms on Cain's part (including a regimental redesignation to the 597th) and success in its first campaign, the regiment pulls together to become a top-notch fighting force.
Amberly also says that Cain has an unusually tight bond with the officers of the regiment, and they come as a comfort to his court marshal at the end of Traitor's Hand.
In James Swallow's Horus Heresy novel The Flight of the Eisenstein, while waiting on a crippled ship to see who the Imperial forces that found them were, Garro, a Space Marine, feels a kinship with the common soldiers also waiting that he had never felt before. When the ship's captain checks what he is saying, Garro urges him to speak: their experiences together should permit candor.
In James Swallow's Blood Angels novel Deus Sanguinius, Solus laments having fired on his battle-brothers. (Indeed, in this novel, Rafen must make it clear whenever he refers to Arkio as his brother that he is speaking of a blood relationship on top of their being Blood Angels; everyone's first thought is of this trope.)
In Red Fury, after disputes between the Blood Angels and the Flesh Tearers — including a duel between Rafen and Noxx — they are sent on a mission. When frantically trying to escape they are last to get on the shuttle, and Noxx gives Rafen a hand up; in the take-off, Turcio sees Rafen help Noxx keep on his feet. Turcio notes what a change it is — and keeps it to himself. At the end, Noxx admits that he dislikes Rafen a little less.
Also in Red Fury, the Flesh Tearer Chapter Master Seth fiercely opposed the request of the Blood Angels Chapter Master Dante and proposed dissolving the Blood Angels, but while they are fighting the Bloodfiends, Seth is knocked so that he is falling in a pit. Shouting "Brother!", rather than "Cousin," Dante grabs him and drags him back. Seth asks if he's worthy of such an address, and Dante asks if he is. At the end, Dante asks the other chapters, again, if they will give him members of their Chapters for the Blood Angels, and Seth declares that they will. He cites the page quote and says that these events have come to pass so that they are reminded that they are not cousins but brothers.
In Dan Abnett's Titanicus, when Mechanicus units plug off to fight Chaos despite a schism, one conspirator who engineered the split complains that this trope means they will continue to follow the man leading them into battle.
In Ben Counter's Soul Drinkers novel Chapter War, Gresk and Pallas are veterans; they join Eumenes's revolt but find it hard to fight battle brothers. Gresk talks to Sarpedon in battle, telling him there is no need to fight, and letting him guess about the orbital attack, and is executed. When Pallas goes to fight Lygris, Lygris thinks he as much wants to be kill as to kill.
In C. S. Goto's Blood Ravens trilogy, Rhamah has his doubts about Ahriman, but wavers because they had, after all, fought side by side against the Harlequins.
In Andy Hoare's White Scars novel Hunt for Voldorius, we are assured in the epilogue that the events of the novel formed this between the White Scars and the Raven Guard. Although the last actual scene shows that the Raven Guard vanished, leaving the White Scars with plenty of questions, taking the woman who had been prisoner, and the White Scars were rather annoyed.
One of the short stories is about how Harry met Murphy. He had been hired to track down a runaway child, who had wandered onto a bridge which happened to have a troll living under it. Murphy was nearby to help take it down. In Cold Days, Harry says they've been friends since that moment.
In The Fellowship of the Ring, Legolas and Gimli get along rather better after spending time together in Lothlórien after the Battle of Moria.
My old friend had won to the highest place in the navy of Helium, but he was still to me the same brave comrade who had shared with me the privations of a Warhoon dungeon, the terrible atrocities of the Great Games, and later the dangers of our search for Dejah Thoris within the hostile city of Zodanga.
In Andre Norton's Witch World, Koris and Simon Tregarth, starting with their first meeting. Later the men admit that despite the Falconers' hostility to women and so to the witches, the men of Estcarp have a relationship of less than total hostility, because they're all fighters together.
In Wen Spencer's Endless Blue, Turk, knowing that nothing unites better than a common enemy, intends to keep the new Reds away from his veterans until they have a common enemy to unite them. (It goes awry, but that's his intention.)
Maxie, Rosie, and Earl—Partners in Grime. Three kids who don't initially know each other, and are not inclined to get along (especially since one of them is a huge tattletale), end up ditching school together. They argue and get annoyed at each other, but come out of it as friends in the end.
Good Omens. Crowley, a demon, and Aziraphale, an angel, are quite obviously going to be enemies. However, after an indeterminate amount of time being Enemies, they came to realize that they had more in common with each other than their actual superiors. Thus, they came to an Agreement. They went from thwarting each other's actions to just going about their own business, with little acts of evil and little acts of good here and there, and occasionally holding down the fort for each other, as well as going out for lunch and drinks now and then over the past few millennia. Their part of the plot of the book is siding with each other again Heaven and Hell with the intent of averting the apocalypse. They also get the bonus points for Back-to-Back Badasses and It Has Been an Honor.
On d'Artagnan's first day in Paris, he is challenged to duels by Athos, Porthos, and Aramis. Just as the first duel is about to start the group is challenged by four of the Cardinal's guards. D'Artagnan chooses to fight with the Musketeers, and the quarrels are forgotten when he is instrumental to their victory.
D'Artagnan and Rochefort spend the first book as nemeses. In an epilogue, it's explained that they fight several duels before ultimately becoming close friends. This is almost never carried over into any adaptations.
In Rick Riordan's The Lost Hero, Leo assures Piper that even if Jason regains his memory, their adventures together will assure that they are still friends.
All of the Seven grow into this over the course of the series, by the end of The House of Hades even those of them who were the most unwilling in the beginning are True Companions.
Vorkosigan Saga: In Lois McMaster Bujold's Cryoburn, Miles explains their connection to Raven as this, through his and Roic's being kidnapped and escaping together — covering up their older connection.
Conan the Barbarian: In "The Scarlet Citadel" Conan muses at the end that while Pelias unquestionably saved his life, his freedom, and his kingdom (both keeping him on the throne and preventing it from falling under an oppressor), he nevertheless never wants to lay eyes on him again. (Then, Pelias is unquestionably a Necromancer.)
In "The Shadow Kingdom", Kull feels this toward Brule. (No doubt aided by Brule's being the only one he can know is a real man.)
In Dennis McKiernan's novel Dragondoom the two main characters, a female human and a male dwarf, become this. Humans and dwarves hate each other at this point in time and they immediately take a dislike to each other. However, it turns out they are both after the same thing and quickly have to team up to survive attacks from the baddies trying to stop them. Eventually they develop romantic feelings for each other, but never get a chance to say so. Biggest Tear Jerker ending.
A variant occurs in Fablehaven—the two protagonists, Kendra and Seth, are actually a pair of bickering siblings who never truly seem to get along. However, the trials they endure in Fablehaven bring them closer together, and help them to truly understand one another and become a true Brother-Sister Team. (It helps that Character Development occurs on both sides.)
Similarly, The Beyonders by the same author has Jason and Rachel. Although they do connect due to both being "Beyonders" from Earth, Jason is stubbon and Rachel is argumentative, which ends up pretty much like you'd expect. However, they do begin to connect, and Jason gains a great deal of respect for Rachel once she proves just how badly she wants to avert being a Neutral Female.
In Jasper Fforde's The Eyre Affair, Joffy muses how at first the war was pleasant, and the camaderie found nowhere else was a big part of it.
Elfsong by Elaine Cunningham had Danilo Thann and Elaith "The Serpent" Craulnober fighting together. While they did sort of lend each other weapons, the first time Danilo gave no-nonsense Elaith a sword loudly singing "Elminster's Jest" and the second time he grabbed the elf's inactive Moonblade (the reason of most pain in his life). Elaith had a foul temper in better situations, and both times was close to killing him after the action. So they eventually became Vitriolic Best Buds.
In Jack Campbell's Fearless, after Geary's ship and two others stay to control a hyperspace jump about to be destroyed, there are rumors that Geary had destroyed it, and the captain of the Diamond, one of the other ships, explodes with rage on hearing — he admits to not having thought well of Geary before, but that's a lie, and he would be proud to fight by Geary.
Bail Organa and Obi-Wan Kenobi in Star Wars: The Clone Wars: Wild Space. They eventually become close friends after driving each other crazy for weeks while cooped up on a starship, surviving the crash of said spaceship at the hands of the Sith, trekking through hostile wilderness, coping with Obi-Wan's reliving of his most horrific memories and keeping each other going despite considerable injuries. The two men end up trusting each other implicitly, despite their considerable differences.
Gavin Darklighter and Asyr Sei'lar. The first meeting between the two nearly results in Gavin getting executed for (perceived) bigotry despite the arguments of former attorney Nawara Ven, but a raid by Imperial stormtroopers intervenes. Gavin instinctively pulls Asyr out of the way just as the raid begins, allowing Asyr to realize she was wrong about Gavin being a bigot. They stick together until they escape the raid, and maintain a strong relationship afterward.
In the Dale Brown novel Shadows of Steel, this happens between Tony Jamieson and Patrick McLanahan. The former is most displeased by having to fly with who he sees as a disgraced now-civilian, while the latter is aloof and mission-focused. They eventually bond during their mission.
In ''War Maid's Choice'' the Sothoii who fought beside the hradani infantry against three devils and a horde of ghouls don't take kindly to insults against their former enemies, and those who fought beside Leanna and the other war-maids in an apparently hopeless defense of the king, including the king no longer find disparaging remarks about them all that funny either.
In Forerunner Foray, when Ziantha escaped the mental Time Travel but Turan did not, she mourns and reflects on how for the first time, she had known an equal, and thought it was like the bond between crewmen or Patrol who had faced a common danger.
In Bernard Cornwell's Sharpe's Triumph, Sharpe reflects on how he and McCandless are as close to friendship as is possible between a sergeant and a colonel — not because of a battle, but because they had been prisoners together.
In Power Rangers Dino Thunder. The three main rangers. High School seniors, Kira, Ethan, and Connor are not friends to begin with. The three end up in detention together then become Dino Rangers becoming frinds in the process. Cassidy Cornell mentions how weird it is that they are suddenly friends.
Power Rangers: Subverted. The main 5 rangers hadn't met prior to becoming rangers and wouldn't have met if they weren't, but all of them become friends because of it.
Power Rangers Megaforce has Gia and Emma who are best friends, Jake and Noah too, and then there's the new kid Troy. Them becoming rangers makes the five of them friends.
In Buffy the Vampire Slayer, this is how the Scoobies became friends. It is also the most common solution to any major strife among the Scoobies. A notable example is Xander and Spike in the final season. Despite openly hating each other until this point, they manage to work together to save the girls from the influence of RJ's magic jacket in 'Him'. After Spike goes back to save Xander from Caleb in 'Dirty Girls' their previous animosity is almost completely set aside. Perhaps the most prominent example is in "Dead Man's Party" during season 3. After just about everyone spends most of the episode trashing Buffy for running away to the point that she nearly runs away again, all is forgiven and they're all best buds again right after they stop a magic mask-induced Zombie Apocalypse.
Pretty standard for the heroes in Angel but Wesley and Gunn deserve special mention.
Gunn: Come on, English! You know you my man!
Angel: So, ah, I see you guys have bonded.
Gunn: Happens when you fight shoulder to shoulder.
Wesley: Or rather hip to shoulder these days.
Gunn: This man took a bullet for me!
Wesley: Ah, it was nothing!
Rome: Lucius Vorenus and Titus Pullo start out as enemies, but their various adventures together quickly turn them into the best of friends. The characters were based on two real life Roman centurions noted in Julius Caesar's journal for sharing a bitter rivalry and yet each saving the other's life in a single battle, making this trope Older Than Feudalism.
In the very first episode of Doctor Who, the Doctor doesn't really seem to like Ian and Barbara very much (the feeling is quite obviously mutual), but he's forced to work with them when the three of them (along with the Doctor's granddaughter, Susan) are captured by cavemen. They manage to win their freedom by showing the cavemen how to make fire. They go on to become very close friends. Their friendship was therefore, quite literally, forged by fire.
Mal and Zoe, to a Platonic Life Partners level. We don't see the exact moment of forging; rather, the war they were in together seems to have been a protracted forging process.
Mal and Simon. They rubbed each other the wrong way because of culture clash, suspicion, and the clash of their highly evolved Papa Wolf and Big Brother Instincts. But they learned to respect each other as the show progressed.
Jayne is a tougher nut to crack, but he and Simon also seem to have reached this point by the end of Serenity.
On Chuck, the members of Team Bartowski started out suspicious and paranoid of each other, but have grown into fast friends, saved each others' lives multiple times, and committed treason (and the occasional thoughtful felony) for each others' sakes.
Heroes: Peter and Sylar have some sort of bond in the realm of friendishness, after having spent five years together in an otherwise empty replica of New York City. Matt protests profusely, going as far as pushing a thought in Sylar's head to prevent him from leaving. Peter proceeds to defend him, although whether this was because he wanted to help Sylar or so that Sylar could save his friend Emma from helping destroy half of New York City (or maybe just Central Park — it was never very clear just how much of the city would be destroyed).
The West Wing: While the main cast were already like family before the assassination attempt at Rosslyn, the crisis, and the vigil over Josh can be seen as the moment where any loose ends locked into place. Most notable was Mandy's getting Brother Chucked without sharing the characters' ordeal.
In the fifth season Leo's commitment to this trope is put to the test when an old war buddy who saved Leo's life is brought up on corruption charges and Leo is faced with standing by his Fire Forged Friend or doing the right thing.
House: YMMV. They don't literally fight together, but House's team shows the occasional odd glimmer of this. They weather the accurate accusations of drug use, euthanasia, murder, and insanity. They keep each other . . . somewhat . . . sane. No matter what tragedy strikes, they always seem to reform afterward. It's a weird example, but it qualifies.
Farscape — John Crichton and Ka D'argo. In the first season, D'argo tries to kill Crichton several times, and in episode 11 Crichton even says, "We're never going to be friends... We can be allies." After fighting side by side for a couple seasons, they end up being each other's BFF. To a lesser extent this became true of the rest of the crew on Moya over the years. Literally forced together through circumstance and picking up strays alongthe way, the group started out barely tolerating one another and seeking to advance themselves at the cost of the others. By the end, with the things they had suffered through together, even the most selfish like Rygel had gone through fire and blood for their friends.
Secret Diary of a Call Girl: Belle curses out Bambi when she finds out Bambi was stealing clients (and had found her generally annoying besides). After rescuing each other from punters who turned out to be psychopaths, they become good friends; Belle writes Bambi into her book, and later acts as her maid of honor.
Misfits is pretty much made of this trope. Although you could argue that even after being lumped together on community service, getting caught in a freak electrical storm and imbued with godawful superpowers, and then accidentally killing their probation worker and having to dispose of the body, the gang still don't particularly like each other, despite having formed a strange kind of bond.
Also defines Blake's 7 (not that any of them would ever admit it).
Dorian: That's why I came for you. You care for each other. After what you've been through together, you couldn't fail to care for each other. Even you, Avon.
Babylon 5 provides an excellent example in the shape of Ambassador Londo Mollari of the Centauri Republic and G'Kar of the Narn Regime. Hating one another at first for reasons political (the Centauri had previously ruled Narn with an iron fist) and personal, the Centauri invasion of Narn space led at first to a bizarre convergence of interest and eventually a truly Odd Friendship as the series progressed. In the end, a prophecy Mollari had of G'Kar killing him came true in the oddest way imaginable: Londo, by now Emperor, trapped by a Drakh Keeper, has his trusted friend G'Kar kill him as part of a Thanatos Gambit to set the Centauri people to freedom and a bright future under Emperor Vir Cotto.
The Minbari and the humans culminating in an actual marriage between a Satai who voted for the Earth-Minbari war and Starkiller. Not to mention a human going back in time and becoming Valen, and the implication that the humans and Minbari would eventually take the place of the Shadows and Vorlons in guarding the still-younger races—although they would presumably they cooperate, seeing how bad of a job the Shadows and Vorlons did. Joining to fight off Ultimate Evil does that.
Air Crash Investigation: The passengers and crew of British Airways Flight 9 started their own club after their strange and nightmarish ordeal.
In Burn Notice, 2x13, Michael and Bly are dancing toward mutual destruction, when they end up caught in the midst of a bank heist. A few hijinks and a bullet wound later, they decide instead to do each other some favors and leave each other alone.
From the episode Darmok, this trope has an in-universe name: Darmok and Jalad at Tanagra which, by the end of the episode, becomes Picard and Dathon at El-Adrel.
When the Universal Translator can't make sense of their language, an alien leader (Dathon) has himself and Picard forcibly beamed to the planet El-Adrel where they are forced to work together against a vicious beast to survive despite the Translator not working. Picard learns that the alien communicates entirely through analogy and metaphor and Dathon teaches Picard the story of how Darmok and Jalad became friends by battling a shared enemy at a place called Tanagra. Picard then shares The Epic of Gilgamesh with him.
Worf and Martok become very close friends after being held captive by the Dominion, with Worf later joining the House of Martok as a brother.
After seven years of mutual mistrust (and with good reason), at the end of the show, Kira, Damar and Garak have to put aside their differences and work together to create a rebellion that will overthrow Dominion control of Cardassia. Without it, the Federation can't win the war. By the end of the show, it's strongly indicated that the experience led to the beginning of this trope for Kira and Garak. Damar dies.
In Sherlock, Sherlock Holmes and John Watson's relationship develops gradually over the first episode, and the familiar Holmesian friendship dynamic is fully established when John shoots the serial killer to save Sherlock's life.
At the start of Whitechapel, the detectives are a team but almost universally hate their new boss, DI Chandler, who thinks they're unprofessional slobs. Over the course of several stressful but revealing days together, he grows to respect them as real detectives and they decide he's not a such an asshole after all. That doesn't stop the insults, especially between Chandler and Miles.
The Vampire Diaries starts off with Damon and Stefan hating each others' guts, Elena's ex-boyfriend Matt disliking both of them, ... By the end of the second season they are one tight knit group, even the ones that should be mortal enemies like the werewolves and vampires. Each time they get closer, it is because of a stronger enemy. Even season 3s Big Bad seemed like this.
In Hell on Wheels Cullen and Elam have, as might be expected between an ex-slave and a former slave owner, a rocky relationship at the best of times. After Cullen saves Elam from a lynch mob and later on they fight and kill said mob when it pursues them they seem headed towards this.
Once Upon a Time: Red Riding Hood and Snow White become friends while hunting for The Big Bad Wolf. Snow finds out from Granny that Red herself is the wolf, and helps her stop Red before she unintentionally killed more people. In the fairy tale timeline, the next time we see them Red knows Snow's actual name (after Snow had given her an alias until she knew Red could be trusted) and is clearly helping Snow stay in hiding from the Queen. While we have yet to see what happened after Snow drags a confused, human Red away to protect her from hunters, they end up good enough friends that, during Snow's fight to save Prince Charming, Red (along with Grumpy) seems like she's practically Snow's Number Two.
LOST: The plane crash survivors don't always get along, but thanks to their circumstances (and hostility from the Others,) they realize they're in it together. The background characters are wholly apathetic, but the regulars are always going off to rescue each other despite the many dangers. Jack and Sawyer, in particular, hate each other, but still look out for each other against common threats. This is exemplified by their Survival Mantra; "Live together. Die alone." The Grand Finale really makes it explicit how the group had came to relate to each other as true companions, to the extent that none of them would "move on" from the flash-sideways universe until all of them were ready.
Christian: [to Jack] The most important part of your life was the time that you spent with these people. [...] You needed all of them and they needed you.
Stargate Universe starts out far from this, with expedition members distrusting, framing, marooning and betraying each other (okay, so that's mostly two of them), and gradually develops into this. Young finally states this explicitly in the last episode, referring to the crew as a family.
The "seven stranded castaways" on Gilligan's Island. If one of them is in danger, the other 6 will rush forward to rescue them. If one of them is (always wrongly) believed to be dead, the other 6 will be beside themselves with grief. And while they may not be able to get off the island, they are adept at working together to survive whatever life-threatening obstacles are thrown their way. In the end, the answer to the often-repeated question, "Why don't they Just Eat Gilligan?" is obvious. Because they love him.
Smallville: Pretty much all of Clark's friends and loved ones (with the obvious exception of Lex, who goes dark) become this as the seasons go along. Pete becomes Clark's first Secret Keeper besides his parents, Chloe becomes Mission Control and an even bigger confidant than Pete, Lois goes from being Vitriolic Best Buds with Clark to being an integral member of Team Clark and the other half of a Battle Couple with Clark himself by the end, and Clark's superhero friends all end up interacting with Clark's non-powered friends and becoming their friends as well (even one-off character Andrea becomes Fire-Forged Friends with Chloe during the web/DVD extra "The Vengeance Chronicles"). It's no surprise that by Season 10, Team Clark basically feels like one big happy (though still occasionally dysfunctional) family.
NCIS saw Ziva's relationship with Team Gibbs unfold this way. Especially with Tony.
NCIS:Los Angeles Since Deeks was introduced Sam has at best tolerated his presence and Deeks doesn't like him much better. After the events of "Descent" in which both Deeks and Sam were tortured over stolen nukes, Sam has a much higher opinion of Deeks, given that Deeks didn't crack and give up Sam's wife as the undercover operative the Big Bad was seeking.
The original Battlestar Galactica: Sheba doesn't seem to very much like Cassiopeia, who was dating the former's father at the time. The two women then developed a newfound respect and friendship for one another after the attack on Gamoray that left Bojay wounded.
Friendships that transcend all social classes, between people who would do anything for each other, who share hardship as well as happiness and would be ready to die for each other is one of the major themes of Princess Returning Pearl.
On Marvel's Agents of S.H.I.E.L.D., May and Ward both are affected by an Asgardian berserker staff; the kind that brings up the worst memory of your life and turns it into Berserker Rage power. The power leaves after the fight is over, but the memories fade in time, approximately a decade. Since they are the only ones who can deal with it, they become FFF with benefits. Later, May thinks Ward is protecting her during a fight when he really knew she could take out the bad guy if he took the hit. He corrects her attitude by saying he isn't the kind of guy who can "separate church and state."
Most BIONICLE characters who become Toa are strangers at the start but become friends or at least trustworthy allies during their adventures and fights. Most notably, Tahu and Kopaka practically couldn't have been more different, and a lot of time was dedicated to their petty disputes, but at the end, Kopaka came to regard Tahu as a leader worthy of respect. The close friendship between Takua/Takanuva and Jaller is also this, as they only got so close during their exploits in the Bohrok Wars. Matoro might be the saddest example — not long after he came to regard his teammates a friends, he had to perform a Heroic Sacrifice.
The Nexus. Originally, they were rookies on WWE's NXT show, and were thus, competing against each other for a WWE contract. However, they all came to loathe WWE management as they forced the rookies to do humiliating challenges like obstacle courses and keg carrying contests, as well as constant rule changes and unchecked abuse from certain WWE pros that were supposed to be mentoring the rookies. This led to the Season 1 winner Wade Barrett uniting all the Season 1 rookies and leading an assault on Monday Night RAW until all eightseven rookies ended up with contracts.
The quote at the top of the page is exactly the same as alludes to this bit from the St. Crispin's Day speech:
Henry V: We few, we happy few, we band of brothers;
For he to-day that sheds his blood with me
Shall be my brother; be he ne'er so vile,
Cyrano de Bergerac: Wonderfully subverted: Cyrano and Christian’s friendship is not born because they fight against the same enemy, but because they are courting The Ace Roxane, from whose rejection both of them are terribly afraid and must gather all their courage only to face her.
Dom and Marcus were already good friends at the start of the Pendulum Wars, and it escalated to the point that they consider themselves brothers by Gears of War 3. However, this pales in comparison to their friendship with, Anya, Baird, Cole, then Sam, then... it's a lot of people. Surviving a war against Absolute Xenophobes will do that to you.
In Jak II, the original group of four was expanded to eleven when they meet Torn, Ashelin, Sig, Tess, Pecker, Onin and Brutter throughout the course of their stop-the-Baron fight.
The Survivors of Left 4 Dead are a group of strangers that happen to be immune to The Virus that produced the Infected and caused the Zombie Apocalypse. In order for them to survive and reach safety, they must work together as a team, fighting through the zombie hordes and sharing their limited medical supplies.
Marisa and Reimu of Touhou, who have fought together (and each other) since the second game, consequently forging one of the series closest, most persistent friendships. They later form similar friendships with Sakuya in Perfect Cherry Blossom, several youkai in Imperishable Night and most recently Sanae in Undefined Fantastic Object.
Part of Khelgar's loyalty quest in Neverwinter Nights 2 revolves around getting him, Neeshka, and Elanee to become this.
The main cast of Tales of the Abyss definitely counts. Contrast the first third of the game, when Luke destroys Akzeriuth, to the last third of the game, when Anise betrays the party and directly causes Ion's death. In the first case, the party condemns Luke's immaturity and irresponsibility, abandons Luke in Yulia City and only rejoins with him once they're absolutely forced to. Then, twenty hours later, Anise is almost instantly forgiven for her crime, and the entire party agrees to stand by her side for her duel with Arietta. Considering how much betrayal, murder, crisis and conspiracy they've all had to deal with, it's no wonder they've come to rely on each other. It says a lot that one of the party members is a borderline sociopath, and yet he still manages to learn of the Power of Friendship after all is said and done. In fact, he puts their situation best:
Jade: I don't know about "friends," but we do have an awkward bond of sorts.
Tales of Vesperia implies that Yuri and Flynn are Childhood Friends, but the prequel movie sets them more under this trope. They're butting heads constantly until they save each other's lives a few times and watch their beloved captain die.. In the game itself, Brave Vesperia falls under this trope - they go through a lot, but by the end, the guild is as tight as any family.
Tears To Tiara 2. As Elissa and Daphnis blows their own cover and rise up, about to fight the slavers to the death, Hamil and The Party blows their own cover and join in the fight. The latter is the leader of La Résistance and the former are trying to from an alliance with them to resist The Empire. So it's this on two levels.
In Super Smash Bros. Brawl, Marth and Meta Knight are both standing near the same giant blob of Subspace. Meta Knight assumes the worst and attacks Marth, who defends himself, until some Primids attack, at which point they both turn on the Primids and realize they're on the same side. They work together for the next leg of the game.
Also played similarly with both Sonic and Silver in Sonic the Hedgehog (2006). Silver wanted to kill Sonic because he believed him to be the Iblis Trigger, but realizing Mephiles' lies, the two begin to work together in saving Princess Elise from Dr. Eggman.
In Class Of Heroes, The more your team fights and preforms gambits together, the higher their affinity (bond) becomes.
In the beginning of most Final Fantasy games, the team are people thrust together but eventually become this over the course of their hardships.
Zidane says that they're "more than friends - we're a team"), even though most of the characters (namely Zidane & Steiner) don't get along with each other at first. When Zidane discovers his disturbing origin, he tries to leave the gang. Garnet/Dagger, however, convinces him that they'll stay with him no matter what.
Hell, at that time, even Steiner flat-out declares that he will not abandon Zidane, no matter what.
Final Fantasy XIII has everyone at each other's throats from the start. Hope wants Snow dead because Snow caused his mother's death, Sazh tries to shoot Vanille (at her own request) before turning the gun on himself, Lightning just dislikes Snow from the start, and Fang demonstrates that so long as it would guarantee Vanille's safety, she'd set the world on fire and watch it burn.
Garlot and Leon in Blaze Union, a pair of knights who have both been screwed over by the corrupt political system—Garlot growing up as one of the country's much-abused peasants, and Leon having his face scarred and losing his job and standing as an Imperial guard after his parents were executed as scapegoats to prevent a national crisis. The two of them meet, Leon picks a fight, and his shock and humiliation after losing cause him to become positively obsessed with defeating Garlot. One offer of employment from another of Garlot's enemies, many more battles, a realization that Leon is being used, an emotional final confrontation in a burning city, boatloads of Foe Yay, and a race against time on Garlot's part to save Leon later, they are steadfast friends and teammates.
James Raynor and Horace Warfield in Starcraft II hated each other at first, because Raynor was a "pirate" and a "terrorist" and because Warfield was a Dominion general. When the two of them led their attack on Char, and Raynor pulled off a Big Damn Heroes move to save Warfield and his men, Warfield warmed up to Raynor.
Warfield: "You may be a damned pirate, Raynor, but, whatever happens, you saved my boys today... and I won't forget that."
The same could be said of Tosh, although it depends on your choice in the game. All of Raynor's Raiders seems to be this too, as they're all volunteers apparently, as well (to a degree) Tychus.
In the first Starcraft Raynor was valuable ally to the Protoss, especially with Tassadar, Zeratul, and Fenix, and was instrumental in the Overminds destruction.
Halo 3: had the most recent Arbiter, Thel 'Vadam, join forces with The Master Chief, John-117. At first they start out quite hostile towards each other—Chief even shoved a gun right in Arbiter's...mandibles, but by the end they trust each other enough to pull a Backto Back Badasses, and frequently save each other in battle. That and Arbiter is the only one who believes John has not died at end of the game—who is, in fact, stuck floating in space, with no way to get home, and his AI Cortana quickly approaching rampancy. Don't mind me, I'm just sweating from my eyes.
Humanity and the Forerunners, who had historically been at each others' throats (Respectfully for the most part, but still), become this following the firing of the Halos. After spending the entire Forerunner Saga being Fantastic Racists towards each other (humans being "primitive, bloodthirsty animals" and Forerunners "meddling, high-and-mighty Abusive Precursors), both come together to mourn the unimaginable losses they've suffered.
Beyond Good & Evil has Jade and her second partner, Double H. Initially, they work together simply because they're both on the same side and there's really no one else around; while they don't actively dislike each other, Double H's mania is mostly one-sided. They start to become friends in earnest after Jade saves Double H's life yet again, with their bond ultimatly cemented during a Take My Hand moment.
Persona 4's Investigation Team. It's certainly helped by the fact that part of the plot revolves around defeating each others' out-of-control suppressed feelings.
Persona 3's S.E.E.S. also shows shades of this, given Yukari's initial distrust and hatred for Mitsuru (she held the Kirijo group responsible for her father's death) and Ken's desire to kill Shinji and then himself out of revenge.
The party in Mass Effect 2 is pretty much this trope. The members are very different from each other, from very diverse walks of life. Heck, there are even a few disagreements that threaten to tear them apart. But in the end, if Shepard is a good (and consistent) leader, the entire party will make it out alive, thanks in no small part to watching each others' backs during the suicide mission.
The most blatant example of this is Joker and EDI. They spend almost the entire game bickering at each other until The Collectors take over the Normandy while Shepard and the rest of the party are away leaving them the only ones to stop them. After that incident they treat each other as equals (most noticably, while prior to the incident they referred to each other as "Mr. Moreau" and "It", afterwards they switch to "she" and "Jeff"). In the third game, thanks to EDI acquiring a new robot body they can possibly have a Relationship Upgrade.
Mass Effect 2 plays this in an interesting way. In one team you have a human WMD wrapped up in a dangerously sadistic sociopath, a turian who manages to single-handedly become an Enemy Mine for three warring merc groups, one of the homicidal robot Mooks from the first game, a deathly (and deadly) ill drell assassin and essentially a living avatar of asari justice/Death by Sex (depending on your decisions). If it weren't for a greater threat, most of these characters would probably never be in the same room as each other without trying to kill each other. After the suicide mission, most are on at least cordial terms (except Jack, who is still a bitch, but got a little better).
This carries forward to Mass Effect 3 with Tali'Zorah and Legion. Tali, a member of the race that created the geth and have been incredibly bitter about the whole affair (and whose father is killed by Geth just before her loyalty mission in 2, admits to having come to truly trust Legion, and explains that they have had a great impact on her preconceptions of the geth. Tali is one of the greatest advocates for Geth-Quarian peace by the end of the Rannoch mission. All because a geth decided not to start shooting at her but at her foes.
The Citadel DLC in Mass Effect 3 really drives home the point that the entire Normandy crew has become this because of Shepard. It ends with a party with every surviving member of Shepard's squads across the trilogy in attendance. Even characters who never served at the same time bond over their shared experience fighting alongside Shepard. You even get a War Asset from it.
The krogan and turian forces during the fighting on Palaven in 3. The krogan are initially there as the price of having the genophage cured; the most important surviving turian military HQ is on the moon the krogan reached during the Krogan Rebellions that led to the genophage; they have very different fighting styles, social structures and traditions; and they don't like each other very much, to the point where Warlord Okeer's imprints for his tank-bred krogan included a shot of a krogan pulling off a dead turian's face with a crowbar; but a while after you bring them together, you get a codex report of the "Miracle of Palaven", which has both krogan and turian forces cooperating and sacrificing their lives to pull off a coordinated and devastating strike on the Reaper forces. It's possibly the largest defeat the Reapers endure before the endgame. And it's pulled off by two peoples who couldn't stand each other, but have learned to get along through their shared battle against horrible space-thulhus and their armies of cyborg zombies.
In Jade Empire, Dawn Star and Silk Fox often argue, but gain respect for each other after fighting together while Kang blows up a bridge.
In Sabres Of Infinity, your fellow officers, Elson and Cazarosta, may come to view you as this if you maintain good relations with them.
Squad 422 in Valkyria Chronicles III. Since all of them are convicted criminals, each squad member can't give half a damn if the other guy eats a whole serving of gatling gun barrage. But due to Kurt's compassionate nature and the kind of crazysituations the squad have to go through, they slowly become an example of this trope. When Kurt calls for their aid for one last job after the war is over, all of them answer.
In Might and Magic: Heroes VI Duke Slava forms an Enemy Mine alliance with Kraal, an orc warrior, against Toghrul, a shaman who betrayed Kraal's people and has a grudge against Slava's family. One short military campaign and several debates about religion and philosophy later, Slava considers Kraal enough of a friend to offer him several hundred acres of his own land for Kraal's people to settle on.
Caim and Angelus in Drakengard. They hated each other before and after they made their pact, but as they fought together, they started actually caring about each other. The fight against the Wyrm cements this, as Angelus starts feeling "strange new emotions" for Caim, and thanks him for making her stronger than she was before. Afterwards, Angelus tells Caim to not die during their fight with Manah, and becomes the Seal due to her wanting to protect Caim.
BioShock Infinite gives us the Booker DeWitt and Elizabeth, the two main characters. Oddly enough, their relationship starts out rough but all right, then deteriorates when Booker lies about taking Elizabeth to Paris, and Elizabeth states the only reason she trusts Booker is because he's the only way out of Columbia. Their relationship becomes a lot better when Booker consoles Elizabeth about her tears causing Chen Lin's death, and after Elizabeth kills Daisy.
The Shadow Hearts series has a few of them. In the first game, the three main characters don't really get along: James tends to grate on Koudelka's nerves, and Edward can barely keep the peace, but they have each other's backs in fights. In the second game, Yuri and Zhuzhen constantly fight with each other constantly. Yuri and Margarete also have their moments, but they constantly work with each other, and Margarete even looks up to Yuri.
On a slightly minor scale in Psychonauts with Raz and Lili. Raz is friendly toward most campers, but Lili is a bit cold and belittling toward him. When the two realize that they're both having the same prophetic dream due to Oleander's psychic interference, they work together to get to the bottom of it and are a lot more tolerant of each other by the second act of the game.
Sakura Wars 3: When they meet in Episode 7, both the Paris Combat Revue and the Imperial Flower Combat Troop spend quite a bit of time butting heads, even getting into a dance competition in an attempt to prove which is better. However, after they work together to stop Ciseaux and his flunkies from destroying the Eiffel Tower, they become good allies and friends (though the fact that the judges of the aforementioned dance competition decided that both groups of girls won probably also factored into it).
Molly and Galatea in The Inexplicable Adventures of Bob! got off to a very rocky start, but accepted each other as sisters after being chased by a (small) angry mob and the FBI, and getting lost in the woods.
Vaarsuvius and Blackwing, the elf's familiar, In The Order of the Stick. Blackwing resents being V's familiar, due to V's neglect of him, but when they need to co-operate to destroy Xykon's phylactery, they put aside their differences and develop mutual respect.
From the Global Guardians PBEM Universe: Majestic, a hero team sponsored and sanctioned by the British government, was originally a group of perfect strangers from all parts of the British isles, brought together by the government quickly and with no warning in response to an attack by the subterranean Lemurians. The experience made them a true team. Later, the team would move from this to a true Band of Brothers while fighting off the super-terrorists known as Jihad.
Each team in Red vs. Blue starts off the mortal enemy of the other team, and most people on the same team don't like each other either. As the series progresses, though, they wind up having to help one another through a lot of difficult spots, to the point of coming to each other's rescue.
Justice League, "The Terror Beyond": Solomon Grundy fights against the Eldritch Abominations alongside the League, and strikes up a friendship with Hawkgirl in particular. He gets mortally wounded fighting Ichthultu and indirectly rescuing Hawkgirl. She comforted him in his final moments. Hawkgirl still considers him a friend in the much later episode "Wake the Dead".
Solomon Grundy: Bird-nose help Grundy? But Bird-nose and her friends hate Grundy.
Hawkgirl: Grundy help Bird-nose, Bird-nose help Grundy, okay? Excuse me, Hawkgirl smash.
In the first episode this is the way the league is formed.
Subverted in the second season finale of Megas XLR. After the Glorft commander and Coop work together against Coop's evil alternate universe self, the Glorft commander extends his mech's hand in friendship. Just as Coop is about to accept, he trips in his giant mech, and because of that activates a weapon that destroys most of the Glorft's mech army. Naturally, the friendship is called off.
Optimus Prime and Sentinel Prime of Transformers Animated. Since Sentinel is a Jerkass to the nth degree, this trope is more or less the only thing keeping them friends.
Avatar: The Last Airbender : Aang and Zuko are literally Fire Forged Friends, since both of them can firebend. Unlike typical instances of this trope, their progression from enemies to allies was more gradual, involving several battles where they ended up saving each other. It basically went like this:
Up until "The Blue Spirit," Zuko had been single-mindedly pursuing Aang, because he believed he had to capture the Avatar in order to restore his honor. Once Aang was captured by Zhao, however, he knew that all his hopes would be ruined if he didn't do something. Not one to take things lying down, Zuko disguised himself as the Blue Spirit and helped to liberate Aang from his prison, with the ulterior motive of capturing the Avatar himself once they escaped. Near the end of the episode, Aang asks Zuko if he thought they could have been friends had circumstances been different.
In "Siege of the North, Part 2," despite Zuko having battled with Katara and knocked her unconscious before absconding with Aang's body while he was in the Spirit World, Aang refuses to leave Zuko out in a blizzard to die. This allows Zuko to escape with his uncle.
Almost an entire season later, in "Lake Laogai," Zuko frees Appa from the Dai Li, enabling Appa to swoop in at the last minute in a Big Damn Heroes moment, saving the Gaang. It was at his uncle's insistence, but still, he's the one who made the choice.
Finally, in "The Western Air Temple," Zuko, having stood up to his father and proudly declaring that he is going to join the Avatar and his friends, tries to do so, offering to teach Aang firebending. They completely reject him. Near the end of the episode, he proves his intentions are true by helping to save them from Sparky Sparky Boom Man Combustion Man, the assassin that he hired at the beginning of the season. When Aang sees that Zuko understands what a tremendous responsibility he has vowed to take on, he seals their friendship with: "I think you are supposed to be my firebending teacher."
Similarly, Zuko's going on "field trips" with Sokka and Katara, to break their father out of prison and find their mother's murderer, respectively, help them overcome their distrust out of them.
Subverted in Code Lyoko: in the beginning, the kids weren't very loyal to each other, and worked more like a team of convenience than friends. They never hesitated to kick someone out of the group when they crossed a line, such as when Ulrich used the Time Travel program to cheat on the lottery, and when XANA convinced them Jérémie was toying with their safety. In fact, XANA's plots frequently involved trying to break the team up, and worked quite well each time, for a while. Thanks to Character Development, though, things have changed, especially in the Season 2 finale. On the up-side, this provides a pleasant break from The Power of Friendship message that's reiterated Once an Episode in most Five-Man Band shows. It's worth noting that before coming together as a team, Jeremie and Yumi were friendless social outcasts and Aelita was trapped in a computer for ten years. Although the fact they're doing it all to help Aelita in the first place brings them right back into Power of Friendship territory. As the flashback episode shows, the reason they are antagonistic to Sissi is because she betrayed that trust. Otherwise, she might be a part of the group or at least a Secret Keeper.
Samurai Jack: Jack and The Scotsman first meet halfway across a ridiculously long (and thin) bridge, each man going in the opposite direction. A fight breaks out as they try to decide who should turn back first to let the other cross, before they are set upon and chained together by bounty hunters. The resulting Enemy Mine results in a rather strong friendship, and they meet again a few times through the series to engage in some Back to Back Badassery.
And this doesn't only apply to Twilight either. Although the rest of the Mane Six had a broad knowledge of each other's existence, with some of them even explicitly shown to have a prior connection (like Rainbow Dash and Fluttershy having gone to the same summer flight camp), many of them (like Applejack and Rarity) would probably not have been friends before the events with Nightmare Moon.
Subverted in the "Mountain of Madness" episode of The Simpsons, in which Homer and Mr. Burns are trapped together in a cabin by an avalanche, when Mr. Burns says, "...once you've been through something like that with a person, you never want to see that person again."
Early in the first season of Reboot in the episode The Tiff, Bob and Dot get into a an argument so bad that they both refuse to ever see each other again. Their friends panic that Bob might leave Mainframe so Enzo enacts a series of Zany Scheme meant to get them to either apologize or invoke this trope, failing utterly on both counts. Eventually they get trapped together in a game, the trope taking full effect and their teamwork saves both the day and their friendship (to say nothing of their unresolved sexual tension)
Ilana and Lance are this in Sym-Bionic Titan. While Octus is more willing to cooperate with them, they hardly know each other at the beginning of the show and conflict with their battle methods in the third episode. It's Octus teaching them how to cooperate, then defeating Mutraddi together that allow them to get along much better.
The Spartans encouraged soldiers to have a good friend so that they'd fight harder to protect them. And if they died, hopefully they'd go Ax-Crazy in a quest for vengeance.
The Thespians refused to retreat from the Battle of Thermopylae, fighting alongside the Spartans in their final stand. The Spartans marveled at this; Spartans were raised as warriors and expected to lay down their lives on command, but the Thespians were volunteer soldiers, mostly farmers and tradesmen. The Spartans saw the Thespian's willingness to sacrifice themselves as a kind of courage beyond even their own, and were very proud to have such allies in their last moments. The world has not forgotten.
The Sacred Band of Thebes consisted of 150 pairs of male lovers under the theory that a man would fight harder in the presence of his lover, so as not to be disgraced. The Sacred Band was tough enough to win repeated encounters with the Spartans but was ultimately defeated at the Battle of Chaeronea in 338 BCE (read: killed to the last man) by a force led in part by a young Alexander the Great in his first appearance as a military commander.
Centurions Lucius Vorenus and Titus Pullo. You know, the pair who became incarnated in HBO's Rome series, except Titus Pullo got demoted to a mere career legionary. In Real Life, an incident is documented in Gaius Julius's memoirs of his Gallic ventures, where the two men who were fierce rivals ended up fighting off a large group of enemies, taking turns to rescue each other, to the cheering of the legion.
Although not a life threatening situation, the cohesion formed by working to achieve superordinate goals (a superordinate goal is a desire, challenge, predicament or peril that both parties in a conflict need to get resolved, and that neither party can resolve alone) was the key of the third phase of the Robber's Cave Experiment, information can be found here, and here.
LA Lakers basketball players Kobe Bryant and Pau Gasol. Their friendship is forged by playing basketball together in the NBA, but was most apparent when they were opponents in the final match of the 2012 Olympics- Kobe as captain of the US team and Pau as superstar of Spain's team. After the US won, the two immediately gave each other a long, tight hug.
Louisiana Senator Judah Benjamin challenged Senator Jefferson Davis to a duel on the Senate floor over a perceived insult. The men worked out their differences without violence and became friends. When the South seceded, Confederate President Davis appointed Benjamin to three different cabinet positions in his government. Benjamin thus became the first Jewish cabinet member in a North American government.
A significant part of military training is to get recruits into this mindset, often by having their instructors play the role of mutual opponent.
A lion, tiger, and bear were under the care of an abusive drug dealer when they were cubs. After they were rescued, they proved to be inseparable and still live and play together twelve years later.
John Isner and Nicolas Mahut played the longest Wimbledon match ever in 2010, taking over 11 hours stretched across three days to finish their first-round match (Isner won 4-6, 6-3, 7-6, 6-7, 68-70). The fifth set alone (eight hours) would have broken the previous match length record. They met again in the first round the very next year, and BBC coverage showed that they had become very close friends after their marathon match.