Soul Fragment

In Speculative Fiction, during a conflict or other key moments, a part of a person's Soul or Power Source is unintentionally transferred to another character via Applied Phlebotinum. This process will often provide Party B with a fraction of Party A's powers, memories, and mannerisms.

Similar to, yet distinct from, a Soul Jar. A relative of Personality Swap and In the Blood

If the two characters are enemies, expect a Not So Different speech at some point. May result in Synchronization.

Anime

 * The clone Kikyo from Inu Yasha owes her entire existence to a spell granting her a tiny fragment of the female lead's soul.
 * The  in Tsubasa Reservoir Chronicle are eventually revealed to be scattered soul fragments of the clone Sakura, and at least one was from Clone Syaoran.
 * Let us just say "Season 4 of Yu-Gi-Oh! GX" and leave it at that, please.

Comic Books

 * In the New Universe comic Star Brand, anyone who has the Brand transferred to them or is healed by the current wielder of the Brand will eventually have it completely manifest in them.
 * Fone Bone and Thorn have a piece of the Locust in them during their conflict in Bone.
 * In Fantastic Four #51, "This Man, This Monster", a scientist uses a "duplication device" to physically model himself after Ben Grimm, but when he sacrifices himself to save Reed Richards, Reed speculates that he may have gotten some part of Ben Grimm other than his skin.
 * In Elf Quest, Redlance and Nightfall join their souls together. This doesn't appear to have any outward effects (e.g., she doesn't gain his tree-shaping abilities) -- they do it so they can never be parted even in death.
 * Later in Elf Quest, Rayek absorbs Winnowill's soul. This has far less benign consequences because Winnowill is thoroughly deceiving and malicious, and Rayek has to constantly struggle to prevent her taking control of his body. And he doesn't always win.
 * Rogue of the X-Men gets bits of people's memory and personality when she absorbs their powers.
 * During the DC Comics storyline Our Worlds At War, Wonder Woman rallies the other Amazons and Darkseid in helping Superman push Warworld into a Boom Tube to the beginning of time. When it's all said and done, Wondy tells Darkseid that she infected him with a piece of her soul, forever a reminder that if he does something nice, it's because a piece of her was in him. Didn't last, obviously.

Film
"Spock: "Remember.""
 * Agent Smith attributes a bit of Neo in him to his survival and powers in The Matrix sequels.
 * The Steve Martin/Lilly Tomlin film All of Me.
 * In The Wrath of Khan, Spock puts his mind into McCoy.


 * Data loads part of himself into his B-4 counterpart in Star Trek: Nemesis.
 * The Green Mile: John gives a "part of himself" to Paul.
 * Exorcist II the Heretic: Reagan has psychic powers as a result of her possession along with the spirit of Father Marrin.
 * Lifeforce: The Space Vampire gave a part of herself to Carlson in order to understand humanity, resulting in a telepathic connection.

Literature

 * Harry Potter
 * J.R.R. Tolkien's notes included the possibility that Morgoth had created the Balrogs and the Orcs out of the fragments of himself.
 * There is some textual evidence for this. It is specifically noted that by the end of the war, Morgoth had become much weaker than he was initially- presumably due to spreading his soul too thin.
 * Morgoth's right-hand-man and ultimate successor, Sauron, did split off part of himself to make the One Ring. This part of Sauron will attempt to overwrite the personality of anyone using the Ring- and eventually, anyone in the general vicinity.
 * Lash in the Dresden Files arguably qualifies, she is a copy of the fallen angel Lasciel, imprinted onto Harry's brain.
 * In Mistborn, hemalurgic spikes can confer upon their recipient a variety of abilities stolen from the person they were killed with, along with a fragment of their soul.

Live Action TV

 * A Freaky Friday episode of Smallville had a piece of Clark left in Lionel after the Snapback swap which cured him and redeemed his character.
 * In the fourth series finale of Doctor Who, "Journey's End",.
 * John Crichton to Scorpius in Farscape.
 * Also Aeryn ending up with residual Pilot DNA might count, as it gives her an instinctive understanding of Moya's systems and the ability to interact with Moya in a way that previously only Pilot could.
 * In Babylon 5, Sheridan carried a piece of Kosh for a period after being literally Touched by Vorlons.
 * As did Lyta Alexander. Kosh got around.
 * Which lead up to the "You're not the only one whose been Touched by Vorlons" Crowning Moment of Awesome.
 * Buffy the Vampire Slayer, with Ben and Glory. It also demonstrated that it went both ways, unfortunately.
 * Previously on Buffy, Willow suggests that perhaps The Master implanted a bit of himself onto Buffy. Xander refers to it as "Mystical Bad Guy Transference Thing".
 * In the Star Trek: The Next Generation episode "The Offspring", Data transfers Lal's memory core into his neural net after her emotional overload. He is able to use a contraction for the first time afterwards.
 * An episode of Eerie, Indiana in which an Ill Girl fell in love with a risk-taking skateboarder. When he forgot to Look Both Ways, he died and she got his heart for the transplant she needed. She then proceeded to act like him, skateboarding recklessly and carving graffiti on the desks.
 * Practically the premise of Max Headroom.
 * Highlander Endgame, after Duncan beheads Connor, he absorbs Connor's swordsmanship skills and perhaps a bit more judging my the morphing effect during the final fight were Connor's face is briefly seen over top of Duncan's.
 * In the fifth season of Sliders, part of Quinn's essence gets absorbed into one of his alternates on a different world, due to an experiment by a scientist working on merging worlds. This plot device was the show's way of dealing with the fact that Jerry O'Connell had left the show.

Tabletop RPGs

 * In Mage: The Awakening, mages can create physical objects which are fragments of their souls to gain certain powers. The major downside of this is the consequences should another mage manage to get a hold of your soul stone. Besides being able to drain your Mana, have a strong connection through which to do sympathetic magic, and a degree of access to your own powers, you become the other mage's "Thrall"; essentially, you gain a vague proclivity to performing any task you are set by the holder of your soul stone (although mage traditions hold that you have to give the soul stone back after getting three requests).
 * The predecessor, Mage: The Ascension, ties all magic and the existence of "consensus reality" to the Avatar, a fragment of divine consciousness that exists in all humans. The "Sleepers" are mortals whose Avatars merely filter consensus through to define reality, whereas the mages have "Awakened" Avatars that allow them to twist reality to their liking. There are also a couple of merits (Twin Souls, Shattered Avatar) where your Avatar is part of a matched set.
 * The titular Exalted receive their powers through a "third soul" that effectively grafts itself onto their consciousness. Solars, Lunars, Sidereals, Abyssals and Infernals all receive these shards, and usually experience memories from the lives of past shard bearers. Alchemicals have Exaltations made of refined souls that are "installed" with them at creation. The only exception are the Dragon-Blooded, who usually receive the Exaltation through familial lines.

Video Games

 * In Twilight Princess, Zelda transfers her magical powers to Midna at a particular point in the game, which at the end.
 * Persona 3: When, he gets a small piece of her life-essence. In-game, this translates to an automatic ability that recovers a small amount of HP.
 * And in a reverse instance: after spending ten years to become sympathetic to their plight, giving them a choice about The End of the World as We Know It, and.
 * In Baldur's Gate II: Throne of Bhaal, the main character is forced to give a piece of his/her soul to fellow bhaalspawn in order to enlist his aid. Alternatively,  can part with a piece of her soul in the main character's place, which, provided you bring both along, causes a later banter about if the soul piece has made  feel any different, to which he replies that he's gotten slightly more fond of the colour pink than he seems to remember being previously, as well as fretting about his weight and possibly having an acne breakout. He also gets her memories of, which naturally don't bother him at all... but does spook her when he brings it up.
 * The entire first half of Tales of Hearts is about what became of the various fragments of Kohak's soul. An astronomer absorbs her fear, causing him to fear that the moon is falling; an artist absorbs her doubt and thinks everyone is out to cheat her; a noblewoman absorbs her sadness and wants to commit suicide, etc.
 * In City of Heroes: Warwolves, Galaxy troopers, and Void Hunters are made by implanting a Nictus fragment into the body of a human being. These fragments are the remains of a deceased Nictus and are shown to still have a life of their own.