Sharing a Body

"O'Malley: Shut up, get out of my head!

Doc: Technically it's my head. But I don't mind sharing. Don't you remember that talk we had about sharing?

O'Malley: Shut up!"

- Red vs. Blue

As a result of magic, Applied Phlebotinum, or just plain old plot demands, two characters end up sharing a body. Distinct from Puppeteer Parasite and most cases of Demonic Possession in that the two characters are more or less equal partners here. (The one whose body it is may claim seniority, but enforcing it is a different matter). Sometimes (especially in animation) both characters' heads will be on one body.

Bonus points if the characters in question are diametrically opposed or just don't like each other much, in which case it becomes a form of Chained Heat. This can also be quite interesting if the two sharing a body are of opposite genders.

May resemble Split Personality, but usually happens to characters who have already been well established separately and is almost always a temporary situation. If the characters battle for control of the body, this can share some features with Enemy Within; the key difference is that Enemy Within originates, well, within its host, while the character Sharing a Body does not. Sometimes The Mirror Shows Your True Self, revealing the extra driver.

Anime and Manga

 * In the anime/manga series Birdy the Mighty, an alien cop has her body used to contain the mind of a teenaged Earth boy she accidentally killed. Notably, the body changes appearance based on who's in control at the moment.
 * Akito and Agito from Air Gear
 * The power of Geass in Code Geass
 * Occurs in Sorcerer On the Rocks, apparently with such frequency that no one in the group is surprised by it anymore.
 * Ichigo and  in Bleach.
 * The "Yamis" from Yu-Gi-Oh. Well, two of them. Yami Marik is less this and more a Super-Powered Evil Side taking control. It also is sometimes not fully clear whether normal Bakura is still around or if Yami Bakura is putting on an act. Actually, at one point regular Marik starts sharing a body with Yami Bakura. That's possibly three minds in one body.
 * Yu-Gi-Oh GX also has Yubel, which is more along the lines of possession.
 * A variety occurs in Kurau Phantom Memory, where Kurau carries her Rynax-pair within her body. Alas, her pair is unconscious from the trauma which separated them previously and it takes ten years for her to awaken. She gets her own body when she finally does.
 * Digimon Tamers share their body with their Digimon in their Mega form.
 * Piccolo from Dragonball Z, merging with Neil and Kami.
 * In The World God Only Knows, the  are an example of this, coupled with The Mirror Shows Your True Self.
 * The Jinchuuriki of Naruto can be considered this.
 * Dark/Daisuke and Krad/Satoshi are examples of this from D.N.Angel
 * Fullmetal Alchemist has Ling and Greed who share Ling's body and early on they continously struggle for control. After a while they start to work together and the line between them becomes blurred.
 * Sengoku Youko has Shakugan - who is actually Shakuyaku, a human girl and Kagan, a rock demon in one body. Unlike most examples, both are permanently stuck together and have an amicable relationship and have taken to referring to themselves as Shakugan as acceptance of their status.
 * Yumekui Merry. The relationship between Dream Demons and their host varies from full-time Grand Theft Me (Landsborough), to more occasional Demonic Possession (Chain Noir and Chaser John Doe), to this trope (most notably Engi Threepiece).

Comic Books

 * DC comics character Firestorm is in fact two people who combine to form the superhero and share one body while doing so.
 * Marvel's Thor seems to do this post-Ragnarok with Donald Blake, as they often converse, and seem to swap off depending on the scenario at hand.
 * In The Metabarons, Steelhead shares his body with Krleza the poet. Implanting Krleza's head creates a composite personality that they name Melmoth. Melmoth refers to himself as "I/we," and combines Steelhead's warrior ethos and skills with Krleza's poetic genius and ability to love. Of course, since Steelhead is a Metabaron, this does not end well at all.
 * X Men foe Johnny Dee is a baseline human who shares his body with his conjoined mutant twin. Johnny despises his brother's existence since he had to go through life with a horrible tentacle face in his chest, but has no qualms about using his brother's powers to manipulate and kill the people around him.

Eastern Animation

 * In Technotise Edit I Ja, Edit has to share her body with Edi,

Fan Fiction

 * The representatives of the Well of Souls in Points of Familiarity.
 * Became a plot point in DC Nation. The Titans had recovered a Empty Shell clone of Tula (Aquagirl I), and one of Tempest's spells misfired, causing her and Tempest to be...sharing quarters. It led to some tense moments as well as some Power Perversion Potential (After all, Garth was divorced, Tula was willing, and the pair never stopped loving one another). Aphrodite thought the situation was cute, and intervened to put Tula into a body of her own so the two lovegirds could get it on properly.
 * In the Pony POV Series, the "Discorded" version of Fluttershy created by Discord remains after his defeat as a seperate entity inside her named Fluttercruel. While at first Fluttershy does want to be rid of her and Fluttercruel wants to take over, Fluttershy quickly realizes Fluttercruel doesn't know any better than what Discord created her to be. So Fluttershy decides to first teach her to be nicer and then coexist peacefully. Eventually the two have sharing a body down and work off one another in some situations to get the job done when neither of them could on their own.

Film

 * The Steve Martin film All of Me has his character accidentally sharing his body with a Rich Bitch played by Lily Tomlin.
 * The movie The Thing With Two Heads has a bigoted white man's head grafted onto a black man's body, leading to Chained Heat hijinx as they battle for control.
 * The plot of Being John Malkovich is based on this.
 * In the movie Heart and Souls Robert Downey Jr.'s character must play temporary host to four ghosts to allow them complete the unfinished tasks that will allow them to move on.
 * In the film Shorts, Toby's mom and dad end up sharing a body after the mom makes the wish that they would be "closer together. Really close."
 * Star Trek III the Search For Spock reveals that You'd think there'd be a lot of Chained Heat but they play it classier than that.
 * In Man With the Screaming Brain, Cole and Yegor share Cole's body after Yegor's Psycho Ex-Girlfriend Tatoya murders Yegor and nearly does the same to Cole. A Mad Scientist repaired Cole's brain with the dead Yegor's brain tissue -- the end result is mostly Cole with Yegor riding shotgun and giving him advice. In the end

Literature

 * in The Bartimaeus Trilogy, just before the Crowning Moment of Awesome for both of them.
 * Good Omens: Mistaken for a demon, the angel Aziraphale is exorcised (sort of) and bounces from body to body as he tries to make his way back to England -- first ending up in the body of an Aboriginal Australian boy, then a Haitian witch doctor, then an American televangelist, and, finally, to Madame Tracy, a medium (and Painted Jezebel). They have a cup of tea and calmly discuss the situation while Aziraphale is still in Madame Tracy's head.
 * Robert Heinlein's I Will Fear No Evil (with the complication that it is left ambiguous whether Eunice's mind actually remains present after Johann's brain is transplanted into her body, or whether Johann is experiencing a sustained delusion to that effect).
 * Cassie and Aldrea in Animorphs #34.
 * Vree the assassin does this with both her brother and her enemy (fortunately for her, not at the same time) in Tanya Huff's Fifth Quarter and No Quarter. Not just a plot point, here--it's more or less the central conceit.
 * The sixth Apprentice Adept novel, Unicorn Point, has the magic-based world of Phaze and the science-based Photon merge, resulting in 99% of the population of both worlds sharing bodies with their otherworld counterparts. Most humans (excepting those who hadn't been on Photon for long enough) had direct doppelgangers to merge with, while non-humans (werewolves, vampires, robots) merged with their closest counterparts. Seriously.
 * The same thing happens at the end of the third book, though only long enough to wrap up a few plot points.
 * Rand Al'Thor and in the Wheel of Time series, with the latter mostly gibbering inside the former's brain.
 * This is the entire premise of The Host.
 * "Concepts" in Perry Rhodan were this trope for a while -- a number of human minds (typically seven when first introduced) jointly occupying a single body, which originally belonged to one of them. The canonical and, among fans, probably best-known example is Kershyll Vanne, a former elite intelligence agent teamed up with six experts in their own disciplines in this fashion to undertake missions for the Sufficiently Advanced Alien who came up with the idea.
 * In the obscure SF novel Black Star Rising, a scientist now nicknamed Manyhead nearly died of brain damage that was treated by transplanting part of a dead boy's brain as a replacement for what he lost. When asked his name, he gave it, then a breath later gave the name of the dead boy. Once their initial confusion wore off, they found that they enjoyed each other's company, and that their pooled knowledge improved the quality of their scientific work. When the story begins, they've had so many transplants that they had to undergo experimental cranium-enlargement surgery to fit all of them in.
 * Matthew and the angels in A Madness of Angels... though they seem to be fused so thoroughly that it's debatable whether they count as more than one personality anymore. The only evidence of a distinction between them is that the first-person narration switches constantly between singular and plural pronouns (sometimes in the same sentence), which confuses the heck out of the other characters when it slips into his/their dialogue.
 * Ghosts in the Incarnations of Immortality series can share bodies with the living, as can the Incarnation of War. Two characters who die and become ghosts during the course of the series spend most of the seventh book sharing a body with a living girl.
 * At the end of Please Don't Eat the Teacher, a boy named Will and a dinosaur he met while time-traveling end up like this. The dinosaur is in love with a girl who went time-traveling with Will, but Will is weirdly okay with this, and so is the girl. They do seem to be fusing, though.
 * Fallen Angels have this as their shtick in the Dresdenverse. The Knights of the Cross were formed for the express purpose of helping the host exorcise the demon.  becomes the first person known to have auto-excorcized one of those Fallen Angels.
 * Done rather darkly for a young adults series in Gone where  ends up sharing a body with   They both completely hate their time together and eventually
 * Professor Quirrell and Lord Voldemort did this during Harry Potter's first year of Hogwarts.
 * Near the end of Redeeming The Lost, Marik  Instead of sending him "screaming into madness", , and they both hate the summoner who brought them to this point, so they seem to coexist harmoniously enough. It's portrayed in an interesting way by the first-person narration. Sometimes they are "we", but there's an I-Marik and and I- who remember or want things, though they are both aware of each other's all.
 * Professor Quirrell and Lord Voldemort did this during Harry Potter's first year of Hogwarts.
 * Near the end of Redeeming The Lost, Marik  Instead of sending him "screaming into madness", , and they both hate the summoner who brought them to this point, so they seem to coexist harmoniously enough. It's portrayed in an interesting way by the first-person narration. Sometimes they are "we", but there's an I-Marik and and I- who remember or want things, though they are both aware of each other's all.

Live Action TV

 * The Tok'ra in Stargate SG-1 alternate control of the body between the host and the symbiote. Best not to think about the sex.
 * Actually, that's addressed in Upgrades. SG-1 are used as test subjects for a Tok'ra scientist. The symbiote fancies Daniel, but the host prefers Jack. Both are quite disturbed by this.
 * And apparently the host won the battle and they were going after Jack.
 * The Goa'uld, being the same species, are also capable of this, but they never willingly give control to the host.
 * In the Stargate Atlantis episode "Duet", Lt. Laura Cadman's mind shares McKay's body with him. Hilarity Ensues.
 * In Kamen Rider Den-O, protagonist Ryotaro is occasionally taken over by his Imagin partners - often because they lack a physical form in the real world and possessing him is the only way they can stretch their legs. There are other times when he allows them to possess him, most often when he enters battle, since without their abilities Den-O is pretty well useless.
 * Later on, Kamen Rider Double's whole gimmick is this, being billed as the first Rider made from two people.
 * In Buffy the Vampire Slayer, Glory, an immortal god from another dimension and Big Bad of Season 5 shares a body with Ben, a human doctor-in-training. In this case, each identity takes on his/her proper form when in control, and has no memory of the other's actions. This separation breaks down toward the end of the season.
 * At least one episode of Star Trek Voyager had the holographic Doctor "hide out" in Seven of Nine's body, allowing Jeri Ryan to ham it up without mercy.
 * Another episode had Seven's mind being temporarily taken over by the personalities of other people assimilated by the Borg due to a malfunctioning Borg device in the area. Among the personalities she got to play with this time, there was a Starfleet officer from Wolf 359, a Klingon warrior who attempted to initiate courtship rituals with B'Elanna, a Ferengi who tried to buy Voyager, a scared child and a Vulcan ambassador. She certainly seemed to be enjoying herself in that one.
 * In one episode of Wizards of Waverly Place Harper and Alex end up sharing Alex's body
 * An artifact from Warehouse Thirteen can force two people into sharing a body, although the body changes shape to reflect the mind that's in charge. The entire ordeal is hard to control, doesn't last long, and ends poorly if it's not reversed.
 * In the Star Trek the Original Series episode "Return to Tomorrow", Spock's consciousness is seemingly destroyed while his body is hijacked by a disembodied alien consciousness. Once the alien is convinced to leave, Spock's body drops dead -- and then he gets up, fully himself, and explains that he was temporarily sharing a brain with Nurse Chapel (who smiles and blushes and makes eyes at him for the remainder of the episode).
 * Has this happen on Pair of Kings when Mikayla ends up sharing Brady's body with Brady and Lanny with Boomer. Ironically Lanny still wants them dead (or at least off the island) even while sharing Boomer's Body.

Music

 * Russel of Gorillaz, in addition to some flat out Demonic Possession, shares his body with his friends who were gunned down by The Grim Reaper one night. In the song "Clint Eastwood" and the remixes to it, they possess him to rap.

Video Games

 * Nippon Ichi game Soul Nomad and The World Eaters has the protagonist fused with the malevolent soul of Gig, the Omnicidal Maniac Big Bad that led the World Eaters on a bit of a genocide 200 years before the game began. Although the main character is mostly in control, Gig isn't willing to go down without a fight and offers the Protagonist his immense powers at various points in the game (at one point offering to boost your level by 2000 so you can easily wipe out the Final Boss at a very early stage), but doing so allows him to completely take over the hero's body: a sure-fire way to reach a Nonstandard Game Over.
 * Liquid Snake shares Revolver Ocelot's body in Metal Gear Solid 2, living on through his severed arm. In MGS 4, they've apparently integrated into one personality known as "Liquid Ocelot".
 * In the fan comic The Last Days of Foxhound, Big Boss shares a body with Liquid, briefly taking over the body entirely.
 * Fire Emblem Radiant Dawn has.
 * Emil and his Super-Powered Evil Side from Tales of Symphonia Dawn of the New World, at one point   hijacks Emil's body after saving him... for about the billionth time.
 * In Valkyrie Profile 2: Silmeria, the Valkyrie is reincarnated in the body of a human princess named Alicia as punishment for defying the will of Lord Odin.
 * Sora of Kingdom Hearts is sharing a body with, and has been since he was a young child. Said person doesn't ever use the body, for some reason- Sora's more than nice enough to lend it, too. There's at least one other person in there, maybe two, but they're more properly split personalities.
 * Sora is the series' favorite victim of this trope: He also unknowingly shared his body with  for most of the first game, resulting in him having   all the time. Also, Riku shared his body with   at one point, but the two of them were constantly (and often successfully) trying to surpress the other, so that usually only one personality showed for a long time, before the other popped up again.
 * As of Birth By Sleep and 358/2Days, Sora is sharing his body with not one, but three different (probably dormant) "individuals".
 * One interpretation for a character in Vampire: The Masquerade Bloodlines. No way to tell for sure with a Malkavian, but the circumstances of her/their turning could have permitted it.
 * Sam and Max shares the body of a Frankenstein's monster in the game Night of the Raving Dead, though, being Heterosexual Life Partners, the worst argument they have is about who made a better quip.
 * In Ratchet and Clank: Quest For Booty
 * Iris from Princess Waltz.
 * in Shin Megami Tensei: Devil Survivor.
 * The Prince's dark ego in The Two Thrones, given voice by the Sands infection, which leads the Prince to debate his morality with it over the course of the story. At times the Dark Prince gains control of the Prince's body as well (morphing into a sand-monster with charred skin, burning eyes and a 3-meter razor chain for breaking necks, platforming and some fancy "hurricane of blades" combat moves). At the end of the game
 * Ni GHTS and his sibling Reala have the ability to "dualize" with Visitors, which enables them to fly freely in the Nightmaren's form.
 * This is the premise of Rune Factory Oceans; the protagonists, Aden and Sonja, wind up trapped in the same (Aden's) body and remain that way until Sonja's body is recovered toward the end of the game.

Web Comics

 * Originally, the cyborg commando bounty hunter DoytHaban from Schlock Mercenary, a violent idiot (Doyt) with a high-grade AI embedded in his spinal column providing him with precision weapons control (Haban). Haban was eventually given additional control over Doyt's body, the pair were duplicated, Doyt was shot out of one of the copies (Haban survived), and DoytHaban was (presumably) destroyed by the Government Conspiracy.
 * At one point, there were (briefly) three separate characters who acted like this: DoytHaban, Massey Reynstein (the company lawyer with a partial cybernetic connection to the Partnership Collective Hive Mind), and the AI Ennesby (whose "body-of-sorts" was taken over by another AI, the mind of the warship Sword of Inevitable Justice). Lampshade Hanging ensued.
 * Laz'r'us Nanobots seem to be able to do this, as does Schlock's 'memory reboot', and Petey does it to a number of the Toughs when he tries to undo the mindwipe they got from the UNS. It's debatable whether the fleetmind counts.

Web Original
"Church: So, Doc. I see you're still swimming around in that head somewhere.
 * O'Malley and Doc in Red vs. Blue, as quoted above. O'malley, an evil AI, usually takes over people's bodies via their radios. However, when he infected Doc, it seems that he couldn't completely suppress the pacifist medic's personality. O'Malley has control over the body, but Doc is free to speak. This results in frequent Gollum-Smeagol-like conversations as Doc tries to change O'Malley's evil ways and O'Malley tries to get Doc to shut the hell up.

Doc: Well, it's not the ideal situation, but every relationship need mutual trust and -

O'Malley: We're not in a relationship! I'm simply using your body to fulfill my evil plans. When I'm through, I'm going to throw your rotting carcass into the swamp and let the beasts feed on your entrails! Mwa ha ha ha!

Doc: 'sniff' I love you too, buddy!

O'Malley: Oh, shut up!"

Western Animation

 * Cartman and Kenny for a few episodes of South Park after Cartman drank Kenny's ashes under the mistaken impression that it was chocolate milk mix.
 * Futurama and The Simpsons both had instances in which a head was placed in the body of another person and shared the body that way. Futurama with Fry's head on Amy's body, and The Simpsons with Burns' head on Homer's during a Halloween episode.
 * Another Halloween episode ends with Homer living inside Burns, causing Burns to have a life-sized Homer-shaped bulge in his side. Homer complains that he needs a mouth-hole so he can eat and Burns sings I've Got You Under My Skin to cheer him up.
 * Happened in the Spongebob SquarePants episode "SquidBob TentaclePants" between Squidward and Spongebob, as a result of Tele Frag.
 * Played for laughs briefly in "Can You Spare a Dime?"
 * The two-headed dragon in Quest for Camelot.
 * Speaking of two-headed dragons, don't forget Zak and Weezy.
 * In the Justice League Unlimited episode "Divided We Fall", it's discovered that since an early episode of Superman the Animated Series, evil AI Brainiac has been inside Lex Luthor's body, eventually growing to the point where he has as much control of Lex's body as him. Even Flash points out how disturbing the Body Horror Brainiac creates is. As if the sight was enough Nightmare Fuel for you, the combination of Brainiac's abilities and Luthor's creativity is even worse!
 * In Technotise, the protagonist ends up sharing a body with a sentient computer chip that developed an artificial nervous system parallel to hers. In some situations he takes control of her body to help both of them out. He also can influence her sensations, and takes full advantage of Power Perversion Potential.

Religion And Mythology

 * Common feature in some religions, specifically non-Christian faiths that do not automatically attribute mediumship or the existence of a Physical God, among other things, to demonic possession. Arguably, in a case of Irony and of its more fundamentalist partisans not doing the research, Christianity itself possibly even provided an example with its claim that Jesus is God incarnate. Therefore, Jesus would have been a case of Sharing a Body according to it - as would Christians claiming to have accepted him into their hearts.
 * Most animist or spiritualist religions and mythologies are generally open to the idea of this happening.
 * Channelers and spiritual mediums believe this is a part of Real Life paranormal ability. Others, obviously, would beg to differ and consider it a form of dissociative disorder or of outright fakery.
 * In a less "established" example than more traditional channelers or mediums, soulbonders. Unfortunately even less respected and more likely to be mocked or considered insane than channelers and mediums, especially if their soulbond is a fictional archetype or still living.