Blood Brothers

""Although we were born on different days, we hope to die in the same hour of the same day of the same year. On our very souls, we pledge that this will be true.""

- The Peach Tree Oath, Romance of the Three Kingdoms.

""For he to-day that sheds his blood with me shall be my brother.""

- Henry V

This is where two people have made a pact with each other. The reasons for this tend to vary, but most often, it's because one or both of them owes the other his life -- frequently in battle. From this moment on, they are brothers. Brothers in the sense that they will do anything to protect and, if necessary, avenge the other.

Sometimes this is portrayed with the two taking a Blood Oath, cutting themselves to "mix" their blood. Thus, the trope name.

This trope is very common with Proud Warrior Race Guys, as well as a popular theme in kung fu movies. It's also quite popular in Heroic Bloodshed movies featuring The Triads and The Tongs, who have Blood Brotherhood as a central theme of their organization, best expressed through the 36 Oaths that formal triad members take, which basically boil down to "Do not screw over your sworn brothers, or you will get chopped up by lots of blades." Being criminals, however, Triads and Tongs can be just as prone to backstabbing and betrayal as any other criminal organization, which is especially shown in the grittier cinematic portrayals.

Often, Blood Brothers spend so much time with each other that they're Heterosexual Life Partners. See also True Companions, for when a group of people, because of circumstance, are as close as real family would be.

For the musical, see Blood Brothers. Compare to Bash Brothers. A Sub Trope to True Companions. Note that all examples must include an oath, pact, or other explicit bonding; if it doesn't, it's not this trope.

While you can certainly declare yourself a "blood brother" to another, actually performing a blood pact (cutting one's hand and all) with that person is not recommended nowadays due to the risk of HIV infection.

Anime and Manga

 * In the Fushigi Yuugi series, Genbu Celestial Warriors, Hikitsu and Tomite are the classic pair.
 * The whole Koihime Musou is about this, being based off of the Romance of the Three Kingdoms.
 * Simon and Kamina from Tengen Toppa Gurren Lagann.
 * The manga Gorgeous Carat has Ray and Azura who became blood brothers as kids, complete with mixing of blood.
 * In One Piece, it has been revealed that Luffy, Ace and Sabo were this trope. None of them were related of course, but they were very close and even made a ceremony of drinking sake and became brothers.
 * In Nurarihyon no Mago, the youkai make pacts amongst each other to be sworn brothers.
 * The cast of K-On! are one of the rare female versions of this trope.
 * Similarly, the Four Girl Ensemble of To Aru Kagaku no Railgun also count.
 * Diva's Chevaliers in Blood Plus refer to each other as blood brothers since they have all been turned into Chevaliers because of Diva's blood.
 * Reinhard and Kircheis in Legend of Galactic Heroes are this along with Heterosexual Life Partners. Their friendship started out when Reinhards sister (whom Kircheis is in love with) asks Kircheis to be his friend. It Gets Worse and Reinhard asks for Kircheis help in conquering the galaxy. And so the two rise up in ranks, Reinhard as the shining star and Kircheis supporting him from behind.
 * In Saint Beast, Judas repeatedly asks Luca to stand by him, and when he tries to do things alone Luca reminds him that alone means both of them.

Comic Books

 * G.I. Joe: Joe has Snake Eyes and Storm Shadow, who are the equivalent of Blood Brothers ("sword-brothers") and have indeed saved each other's life in battle. Sometimes even while actively trying to defeat/kill each other. Heavy on elements of The Only One Allowed to Defeat You, Enemy Mine, and, the latter on Storm Shadow's part (at least when they're on opposite sides).   is an integral part of their backstory.
 * There's a pair of Marvel Comics villains known as the Blood Brothers, who are formidable separately but increasingly unstoppable the closer they are to one another.

Fanfic

 * Happens sometimes in Knights of the Old Republic fanfics (more for the first than the second) with Canderous and the Player Character...but sometimes all the crew gets marked as vode. The Mandalorian language doesn't make the distinction between "friend" and "family member" after all.

Film

 * The film version of Othello has Othello forcing Iago to perform a blood pact.
 * A Better Tomorrow: Mark Gor (Chow Yun-Fat) and Sung Tse Ho (Ti Lung) from John Woo's film are probably the best known examples of Blood Brothers in a Heroic Bloodshed movie. In fact, most of John Woo's Heroic Bloodshed movies tend to have two characters develop such a bond with each other during the course of the movie.
 * The 2007 Chinese move The Warlords (starring Jet Li, Andy Lau, and Takeshi Kaneshiro/Jin Chengwu) has the three actors' characters playing sworn brothers along the lines of the Peach Tree Oath quoted above, but with tragic consequences since it doesn't hold nearly as well.
 * Bullet In The Head, Woo's grimmest and most emotionally devastating movie, is about the disastrous effect of Gold Fever and the horrors of The Vietnam War on the bond between Blood Brothers, which in John Woo's other movies was all but unbreakable.
 * In the 2009 Sherlock Holmes film, a fortune teller reads Watson's palm and refers to "two brothers, not of blood but of bond". While this trope is probably true of them anyway, her actual statement is suspect
 * An old Bud Spencer spaghetti-Western, where the (anti)hero, played by Bud Spencer, had a rather dim Native American sidekick, who followed him around due to them being 'Blood brothers', since Bud had once saved his life with a blood transfusion.
 * Star Wars: Han Solo and Chewbacca are Blood Brothers. While Han Solo most likely didn't think so when he first rescued Chewie, Chewbacca felt he had a "life debt" to Han. At first the "brotherhood" was mostly one way but as they traveled together and Han learned more about Chewie and the "life debt", they became true Blood Brothers.
 * According to the liner notes on the Blues Brothers album, Jake and Elwood Blues, unrelated orphans growing up in the same dismal orphanage, swore an oath of Blood Brotherhood by cutting their fingers with an E-string allegedly from Elmore James's guitar, essentially adopting each other. The Mission From God came later. According to the book Blues Brothers: Private, they also had their names legally changed in 1962, taking the same last name and taking each other's first names as their middle names. The Mission From God came later.
 * In Mongol, two ten year olds (one of whom is the future Genghis Khan) become blood brothers after one saves the other's life.
 * Interesting twist in Practical Magic, where a pair of sisters swear bloodbrotherhood. This becomes a plot point a couple of times.
 * In Son of Rambow, Lee Carter decides he and Will Proudfoot should become blood brothers after he saves Will from drowning.
 * In the Taiwanese gangster film Monga the main character becomes blood brothers with his four best friends in a ceremony that echoes the Peach Tree Oath.
 * The Outlaw Josey Wales takes a Blood Oath with Comanche chief Ten Bears to seal the peace between Ten Bear's Comanche tribe and Josey's "tribe" of white, Native American, and Hispanic settlers, implicitly making them blood brothers as well.
 * In Wild Zero, Guitar Wolf cuts Ace's hand and his own to make them "rock 'n' roll blood brothers," and gives Ace a whistle to use if in distress.

Literature

 * Commonly seen in Wuxia literature.
 * In Robert A. Heinlein's Stranger in A Strange Land, the Martians have what is called a "water brother." If you "share water" with someone, from that moment on, you are their brother.
 * While water doesn't seem all that binding on a planet that is two thirds water, for the Martians it is a very valuable and limited resource and to share it with someone is a precious act of camaraderie.
 * In Diana Wynne Jones's The Spellcoats, Kars Adon and Hern make a pact of undying friendship after Hern helps free Kars Adon's people from Kankredin. he points out that they're now quite literally blood brothers.
 * The Indian in The Cupboard: Little Bear and Boone, became Blood Brothers by having their wrists cut and then bound together.
 * In Darkness Visible Marsh and Lewis definitely qualify as this. Once they stop hating each other, that is...
 * Mercedes Lackey's Tarma and Kethry are Blood Sisters, complete with a blood-mixing ritual of clasped hands. The pair were given a stamp of divine approval from Tarma's goddess when the wounded hands were instantly healed upon contact, leaving distinctive scars.
 * Talia eventually does this with both Skif and Kris. Would've been nice if someone had told Dirk that before he went all I Want My Beloved to Be Happy, but then I suppose we wouldn't have the third book.
 * Mercedes Lackey also uses it in the Tales of the Five Hundred Kingdoms series; in order to stop the Tradition from making her fall in love with her rescuer, Princess Andromeda suggests the idea of becoming blood siblings with George instead. This might have been unnecessary, since George is a woman and it's unlikely the Tradition would make two women fall in love since that doesn't typically happen in fairy tales.
 * Moby Dick: Ishmael and Queequeg.
 * Last of the Mohicans: Natty "Hawkeye" Bumppo and Chingachgook.
 * In Romance of the Three Kingdoms, Liu Bei, Guan Yu, and Zhang Fei swear an oath of brotherhood under the tree of a peach garden as quoted above that lasts for their whole lives. They are not the only sworn brothers in the story (for example, Sun Ce and Zhou Yu) but by far the most famous, and for multiple chapters the extent to which Guan Yu will go to uphold this is a plot point, used both by and against him: in particular, Zhang Liao got Guan Yu to surrender to Cao Cao by saying that he shouldn't go out fighting while the missing Liu Bei might still need him), but Guan Yu conditioned that surrender as lasting only until he found his brother's whereabouts... and then openly rubbed the impermanence of this service in Cao Cao's face. Cao Cao however then made Guan Yu the General Who Doesn't Do Anything, up until his opposing warlord's main warrior was too much for Cao Cao's officers to handle and he was forced to pull Guan Yu off from the bench into his lineup.
 * An Aiel ritual in The Wheel of Time can make you brother and sister, the ritual is shown in detail when Elayne and Aviendha go through it to become First-sisters.
 * As a more literal example, several Borderlander monarchs go well out of their way to meet in person for a ritual of this sort, treated as much more serious than a written treaty.
 * In The Bible, David and Jonathan, make a covenant (pact) and their souls are bound together, making this trope Older Than Feudalism. Jonathan will do anything to protect David, namely betraying his own family.
 * In the Catholic Dogma, our true father is God. Thus, we are ALL Blood Brothers.
 * Judge Dee's three lieutenants, Ma Joong, Chiao Tai and Tao Gan, consider themselves and refer to each other as Blood Brothers.
 * In Conn Iggulden's Emperor series, Caesar and Brutus are blood brothers. 'Course, we all know how that turns out in the end...
 * In his later Emperor series, Jochi and Jebe do the blood mixing thing.
 * The Devil In Vienna has a female example, with Jewish Inge and Catholic Lieselotte copying a blood brotherhood ritual-drinking wine mixed with their own blood- from a western novel. They always sign their letter "B.S.L" for "Blood Sisterly Love."
 * Hagan and Waldhari in Stephan Grundy's Attila's Treasure, especially poignant because of the huge differences between them. As the book progresses it seems as though their devotion to each other only grows stronger the wider the gulf between them.
 * Horus Heresy: Saul Tarvitz and Nathaniel Garro. Instead of mixing blood, they carved an Imperial eagle into their gauntlets. It even states that there is only one member of the Emperor's Children Garro considers his brother - Tarvitz.
 * In Rosemary Sutcliff's novel Blood Feud, English lad Jestyn is sold as a thrall to a Dane called Thormod, but after a few battles they realise they are inseparable. They become blood brothers after a blood-mixing pact.
 * Novels of the Change: The anamchara ritual has this effect. Unlike most takes on this trope, it does not preclude romance.
 * In the Xanth novel Centaur Aisle, two allies are wounded during an unbalanced swordfight, and one says, "Now our blood has mingled; we are blood brothers."
 * The entire point of The Sisterhood of the Traveling Pants. The girls practically consider themselves family being born around the same time and basically spending their entire lives together. It's in the title, man!
 * In Gisle Surssøns saga, one of the Icelandic lineage sagas, the protagonist Gisle makes a pact with his brother Torkel and his brothers-in-law Vestein and Torgrim. The four of them mix blood by each letting theirs flow into a hole dug into the ground whereupon they cover it with a tussock. In this way, they become sworn brothers who must avenge each other if either of them should be killed. It does not end well when Vestein is murdered and Gisle mistakenly believes that it was by Torgrim.
 * Winnetou and Old Shatterhand in the books of Karl May.
 * The title character of the Flashman novels swears blood-brotherhood with several characters, noting in Flashman at the Charge that he felt more solemnity in the act than any Christian oath.

Live-Action TV

 * In Star Trek the Original Series, Kirk, Spock, and McCoy are Blood Brothers. This goes even further in the movie, Star Trek III the Search For Spock, when we discover that Spock managed to.
 * Played with in Buffy the Vampire Slayer, season 5.
 * The Easy Company in Band of Brothers evolves into True Companions by stacking blood brotherhoods one after another.
 * In Hercules: The Legendary Journeys, Hercules and Iolaus have admitted to loving each other as brothers. (The fanfic writers often choose to ignore those last two words.)
 * Though to be fair, Herakles and Iolaos were lovers. Herakles was also Iolaos' uncle.
 * Kamen Rider Kabuto uses this trope most clearly in the form of the Hopper Brothers: Yaguruma Sou (Kick Hopper) and Kagayama Shun (Punch Hopper).
 * Pawn Stars: Chumlee and Corey are very much like brothers. Much to Rick's dismay.
 * Ted declares this for Barney and Marshall in the season three finale of How I Met Your Mother, which causes Barney to start needling him about who's his best brother, in reference to his and Marshall's long running argument over who's Ted's best friend.
 * Coupling has Jeff and Steve who grew up in school together, and have remained best friends even into their busy and commercial London lifestyle orientated adulthood. So close in fact, that they are in fact porn buddies. By Jeff's wording, when one dies, the other is morally obliged to go to their deceased friend's house and remove all of the porn before their family and colleagues find it. He even boldly defends this pact when talking to Steve's future partner to big his friend up. Disclaiming "that's how close we are!"

Music

 * In the song "Goodbye Earl" by the Dixie Chicks, Mary Ann and Wanda are Blood Sisters. When Wanda is put into the hospital by Earl, they get together and kill him.
 * Bruce Springsteen has a song named Blood Brothers which fits this trope perfectly.
 * Iron Maiden has a song called "Blood Brothers" on this very topic. Interestingly enough, their song "The Clansman" about the strong bond between Scottish clan-member evokes this trope even more.

Mythology

 * Norse Mythology:
 * Odin, Chieftain of the Aesir, and Loki, trickster demigod, were celebrated blood-brothers, and Odin would never sit at a table where Loki wasn't welcome. This causes problems when, in the leadup to Ragnarok, Loki's villainy reaches new heights and Odin can no longer remain blind to it.
 * Örvar-Oddr and Hjalmar, two heroes from the legendary sagas who became blood brothers in a ceremony after pouring their blood under some raised soil.
 * In The Bible, David and Jonathan.

Professional Wrestling

 * The famous Anoa'i family, which pioneered the Wild Samoan archetype, was formed by Amituanai Anoa'i and "High Chief" Peter Maivia, two men who did see one another as blood brothers (Anoa'i's children referred to Maivia as their uncle). The family includes Afa and Sika Anoa'i (the original Wild Samoans) The Rock (Dwayne Johnson), the late Rodney Anoa'i (a.k.a. Yokozuna), Solofa Fatu (Rikishi), The Tonga Kid, and Eddie Fatu (known as YOU MANGA Umaga).
 * In one of the 90s episodes of Titanes en el Ring, La Momia cut a ribbon, symbolizing the end of his feud with the late Martin Karadagian, and effectively making them Blood Brothers.

Tabletop Games

 * All Space Marines ever in Warhammer 40000. They even call each other "Brother", constantly, though this may be as much their Catholic Space Nazism somewhat monastic style as their fanatical loyalty to the Chapter and one another.
 * And they have all been sort-of genetically manipulated to be similar to their chapter's Founder, essentially making them his children.
 * For a slightly more heretical version, teams of Tau Fire Warriors go through the Ta'lissera bonding ritual, producing their own squad-scale True Companions. It also gives them sufficient steel in their little blue backs to return even when eight of the original ten are dead, to avenge their fallen blood kin and kick ass for the Greater Good.
 * Dungeons and Dragons. In module CM1 "Test of the Warlords", the PC's can participate in the ritual of blood sharing with a barbarian chief.
 * Changeling: The Dreaming has the Oath of Clasped Hands, which is your standard blood-mixing ritual with in-game results. (Specifically, both parties get an additional point of Willpower for as long as the oath is upheld.) It's described as the platonic version of the Oath of Truehearts, which is expressly for lovers.
 * This is also how motleys usually form up in Changeling: the Lost. Groups of changelings swear an oath on the Wyrd to come together for a common purpose, and usually gain mechanical benefits related to that area on the condition that they stand up for one another and don't flag in their pursuit. Likewise, there are other Oaths that provide similar benefits, such as the Ancient Pact (which is when a changeling swears one of these with a mortal) and the Vernal Oath (which is a marriage oath).
 * In 7th Sea, the Eisen have the concept of the rucken -- which means "back-brother" and is considered the the strongest oath an Eisen can give outside of marriage. The rucken is someone you can absolutely trust to have your back and vice-versa. Woe to anyone who betrays their rucken's trust and willingly breaks that vow.
 * Ars Magica supplement The Order of Hermes. When two mages want to form a bond of amicus (intense friendship), they cut their wrists and place their wrists together to share their blood. Grogs sometimes do this too, and specifically call each other "blood brother".

Theater

 * The musical "Blood Brothers", obviously. It goes very, very badly.
 * Siegfried and Gunther swear blood brotherhood in Wagner's Götterdämmerung, with Gunther's half-brother Hagen presiding. Given that Hagen is evil, it's not surprising that this ends badly.

Video Games

 * Fatal Fury: Bosses Grant and Kain R. Heinlein have 'sworn an oath of eternal allegiance' to each other, as can be seen when they fight in versus mode.
 * The "From this moment, you and I are Sworn Brothers" bit between Darunia and Link in The Legend of Zelda Ocarina of Time.
 * Darunia is also a Sworn Brother with the King of Hyrule himself.
 * Also, Snake's codec call on the Ice Climbers in Super Smash Bros Brawl implies that the Ice Climbers have formed this kind of bond with each other, though they're more like Blood Brother and Sister.
 * Eventually, in Planescape Torment Dak'kon does the Pronouncement of Two Deaths as One with you, effectively making you Blood Brothers until death.
 * An alien species called Hunters in the Halo series always come in pars, and will try to avenge the death of the other. This rarely happens though, as they are both practically walking tanks, unless you happen to be the Master Chief.
 * Hunters (m'galekglo) are actually hive-mind colonies of lekglo worms encased in suits of armor. A bonded pair of Hunters is a colony that got too big for just one suit of armor; so the 'rage' when one dies is more like "Oh, that genetically-modified human over there just killed half our city, let's go kill him back" than vengeance for a slain brother
 * Though if they're hive mind, (And therefore basically the same organism) it would be more like: "That guy jut cut off my arm. I'm going to beat him to death."
 * When the colony gets too large it splits into two separate colonies; they share a bond but each colony is a distinct individual.
 * The Halo 2 manual makes it clear that each colony is a separate individual intelligence (this may have been retconned later). The teams are mated pairs, however that works.
 * Solid Snake and Otacon in the Metal Gear Solid series.
 * Eliwood and Hector from Fire Emblem, right down to the literal blood pact they made as children.
 * Winfield, Thoma and Alberti in Agarest Senki definitely counts as this. They even have a Combination Attack with each other.

Web Comics

 * In Homestuck, Karkat Vantas and his universe's version of Jack Noir team up to overthrow the Black Queen, sealing their pact with a bloody handshake. The "blood" part is especially important here, as

Web Original

 * The Saga of Tuck: The Euro-mutt title character and his Chinese-American friend, Mike, call each other brother when not trading blows. This isn't just rhetoric: This is so far unproven, but it was close.
 * Carmilla and Fey, in the Whateley Universe, even going so far as making a blood pact.
 * In The Gungan Council, Ryori and Ti'Cira went so far as to use blood in their pact to be faithful allies to each other. Darth Apparatus and Chaos Maxtor have a just as binding pact, minus the blood, where Chaos becomes the Darth's soldier while the latter gets functional immortality.

Western Animation

 * Parodied in The Simpsons when Bart and Milhouse became "spit brothers", complete with spitting in the hands and clasping them. Ewww...
 * Used in American Dad, when Stan and his new friend become brothers. The next scene shows them both at a hospital for a blood test, happily showing each other the negative test results.
 * Parodied on The Amazing World of Gumball when Tobias tries to cut his hand open with a blunt stick. It doesn't work very well and he keeps trying to tear the skin well into the next scene.
 * On Young Justice, Gar and Megan refer to each other this way after she gave him a blood transfusion.

Real Life

 * Temujin, who became Genghis Khan, formed a blood brotherhood with his best friend, Jamuqa, which was common in Mongolia at the time. To seal this, they cut themselves, dripped blood into fermented mare's milk, and drank each other's blood. Keep in mind, they were about 10 or 11 years old when they did this. Because Mongols are badass. Incidentally, Jamuqa ended up as Temujin's main enemies in the wars to unify Mongolia. But when Temujin finally captured him, he offered him a full pardon, but Jamuqa refused, suggesting that Temujin kill him. Temujin took his blood-brother's advice, and killed him, then gave him a proper burial. Because he was nice like that.
 * To be more specific, they became enemies because Jamuqa had made his own bid to unite the Mongols. While the two had always supported one another, neither could accept the other's rule; Jamuqa compared it to there being only room in the sky for one sun, and only room in the world for one Mongol lord. Jamuqa also requested he be executed without spilling his blood; Mongol religious beliefs held that dying with your blood hitting the ground cursed you to wander the earth as a spirit. Genghis Khan reportedly strangled Jamuqa himself, crying as he did so. As for the generals who had betrayed Jamuqa to Temujin, they were boiled in oil.
 * A popular item of Filipino history is the Blood Compact (sanduguan in Tagalog, meaning "one blood" or mingling of blood) between Miguel Lopez De Legazpi and the King of Cebu in 1565. A contrast to the Filipino revolutionary organization KKK (not that KKK) initiation ceremony where the initiate would cut open an arm vein and use the blood as quill pen ink to write his name on the members' list.
 * This was done by the leaders of the seven tribes that would eventually become the people of Hungary. The event is referred to as the Blood Pact, an important historical event.
 * In the Chinese historical saga Romance of the Three Kingdoms, the Power Trio of the Kingdom of Shu faction were blood brothers. Specifically, Liu Bei, Zhang Fei, and Guan Yu aka God Of War.