[[quoteright:350:[[Manga/{{Parasyte}} http://static.tvtropes.org/pmwiki/pub/images/heroic_parasyte.jpg]]]]
[[caption-width-right:350:Eat your heart out, John Carpenter.]]

[[TheHero Heroes]] perform amazing feats, save the day and everything's golden. But [[WhereDoesHeGetAllThoseWonderfulToys Where Do They Get All Those Wonderful Abilities]]? The answer is an alien (or demon or robot) latched on and the hero gets some nifty superpowers as a result. Often times this tenant will be a SuperpoweredAlterEgo and [[SuperPoweredEvilSide may not share]] [[DemonicPossession the hero's agenda]].

Different types seen include: Vermiform invertebrates [[ParasiteZombie causing]] [[OurVampiresAreDifferent vampirism]], AdaptiveArmor, ArtificialLimbs, {{Clingy Costume}}s, bystanders, and villains.

This is when a ViralTransformation works smarter and YoureNothingWithoutYourPhlebotinum can actually be true; for the more holistic transformation see FusionDance. Compare with TheSymbiote as it is a similar "other being causes SuperEmpowering" trope. Also compare PowersViaPossession, WillingChanneler; contrast SuperhumanTransfusion and SymbioticPossession.



[[folder: Anime and Manga ]]

* ''Manga/{{Parasyte}}'' has the titular shapeshifting parasites that burrow into a human host's head, eat their brain, and take over the body, resulting in intelligent but emotionless monsters that look human and kill regular humans for sustenance. When the parasites screw up the takeover and end up replacing a different body part than the head, you'll end up with the parasite SharingABody with the human host. This is the case with the main character, whose arm is replaced by a parasite, and the two must learn to work together to fight the other parasites who consider this duo a threat.
* ''Manga/ProjectArms'', cyborg bits with artificial intelligences.
* ''Manga/DGrayMan'', parasite type Innocences are physically integrated into their wielder and so can exert some control over their personalities, but give the hosts incredible powers as a result. The primary user of such an Innocence is [[OurVampiresAreDifferent a mock-vampire due to his Innocence]], which manifest as shapeshifting fangs that allow him to grow stronger by consuming the blood of enemy mooks.
* ''Manga/HellTeacherNube'', although closer to SealedInsideAPersonShapedCan then usual. Although he's extremely skilled and powerful even ''without'' the help of his Oni Hand, many of the [[{{youkai}} critters]] he encounters would be unbeatable or at least extremely difficult to approach without it.
* The Aburame clan of ''Manga/{{Naruto}}'' act as human hives for armies of destructive bugs, who live off their chakra and can swarm and poison enemies.
* In ''Manga/{{Bleach}}'', Ichigo's Hollow powers are the result of [[spoiler:the remnants of the proto-arrancar White that had infected his mother Masaki being passed on to him at birth. These remnants merged with Ichigo's natural Shinigami powers which he inherited from his father and became his Zanpakuto Zangetsu.]]
* Akira Fudo from ''Anime/DevilmanCrybaby'' is currently the vessel of Amon, who is one of the if not the most powerful demon out there. However, he's able to retain his humanity throughout and fights to defend humans, unlike [[spoiler:Miko (whose personality worsened, even if it was temporary and never really got too far) and Moyuru (who eventually defected to the demons' side)]].

[[folder: Comic Books ]]
* In ''ComicBook/CreatureTech'', an alien parasite rips Dr. Ong's heart out, then attaches itself to his chest and serves as a replacement heart. It also provides him with several extra limbs, skills in hand-to-hand combat (the thing can learn kung-fu by watching movies), and when Ong gets really upset, teleportation powers.
* One of the most famous examples is [[ComicBook/XMen the Phoenix Force]], when hosted by Jean Grey (mostly), Rachel Grey (completely), the Phoenix Five (pre SanitySlippage), and Quentin Quire (for a decidedly given value of 'heroic').
* In ''ComicBook/IronMan'', War Machine had at one point Eidolon Warwear, which was basically living technology.
* The artifacts from the Top Cow universe: The Comicbook/{{Witchblade}}, ComicBook/TheDarkness, and The Angelus.
* ''ComicBook/{{Spawn}}'' overlaps this with ClothesMakeTheSuperman; a significant portion of his powers stems from K7-Leetha, the cloth-like demon bonded to his skin as a living costume.
%%* Creator/MarvelComics' ''{{Sleepwalker}}.''
* Creator/MarvelComics' ''ComicBook/CaptainUniverse.'' Different in that that entity bonds with a different person each time, until recently.
* Creator/MarvelComics' ''ComicBook/DarkHawk'' is a young man who literally [[FallingIntoTheCockpit stumbled onto alien tech]].
* Creator/DCComics' [[http://dc.wikia.com/wiki/Jonni_Thunder_(Earth-Two) Jonni Thunder]]: timeshare with an alien energy-being.
* Creator/MarvelComics' [=Sasquatch=], from ComicBook/AlphaFlight, originally thought he was that way due to gamma rays (''a la'' [[ComicBook/IncredibleHulk Hulk]]) but it turned out he opened a doorway into another dimension, through which a Great Beast was able to come through and bond with him.
* The ComicBook/BlueBeetle scarab is a semi-sapient piece of alien tech that is essentially weaponized PoweredArmor: it bonds to a host and encases them in a supremely powerful suit of exo-armor... whilst simultaneously [[MindRape taking over their mind and turning them into a slave-warrior of the scarab's creators]]. Fortunately for the Blue Beetle, ''his'' scarab was damaged before bonding with him, allowing him to retain control.
* Toxin from Creator/MarvelComics, due to having one of {{The Symbiote}}'s bonded to him whilst trying to use it to do good.
* ComicBook/{{Venom}} tries to be this at times, depending on the host (Eddie Brock pulled off a decent [[AntiHero Anti-Hero]], Mac Gargan faked it, and Flash Thompson is this until the symbiote freaks out and starts [[ImAHumanitarian eating things]]). Anti-Venom tries, but Eddie's a little too... [[AxCrazy off in the head]] by now to pull it off for extended periods.
* Comicbook/SpiderMan was this during his time with the symbiote, though for most of their time together he didn't even realize it was in the passenger seat.
* ''ComicBook/SpiderGwen'' didn't start out as one, but after losing her original spider bite-induced powers, the only way she could get them back (and save her friend Harry Osborn in the process) was to create and bond with her universe's version of the Venom symbiote. And while this did lead to a stretch where she had to deal with uncontrollable rage due to the symbiote amplifying her anger over an attack on her father, she was eventually able to work through it and become her heroic self again while still bonded to it.

[[folder: Fan Works]]
* ''Fanfic/ChildOfTheStorm'' has Harry intermittently functioning as a willing host of the Phoenix Force. In the sequel, he [[spoiler: discovers that he can actively use the fragment of the Phoenix inside him as more than just a DefenseMechanismSuperPower. One round of BreakTheCutie too many, however, leads to him snapping and becoming the Dark Phoenix.]]

[[folder: Film ]]
* ''Film/ResidentEvilApocalypse''. The T-Virus gives Alice super abilities, which she uses to fight zombies.
* ''Severed Ties'' (1992): A desperate scientist injects himself with a reptile based regeneration serum to return his arm count to two, which worked out fairly well as long as one didn't mind the mouth, or teeth, or eyes ... and fed it.

[[folder: Literature ]]
* In ''Literature/DisAcedia'', most of Shroud's powers come from Shade/Manah, the manipulative spirit inhabiting his cloak.
* ''Literature/ParasiteEve''. For the most part, the Neo-Mitochondria (Mitochondria who have developed a HiveMind sentience) are simply TheVirus, but in a few people with just the right DNA (read: Aya Brea) it instead becomes a powerful, symbiotic force, granting SuperStrength, HyperactiveMetabolism, Pyrokinesis, and the ability to kill people on the cellular level with your MIND. And probably pick out winning [[SuperpowerLottery lottery-tickets]], too.
* ''Literature/DarkFuture'': Krokodil becomes the Host of the Ancient Adversary, the Pawn of the Nullifiers. Exactly what the nature of the Ancient Adversary is is never made entirely clear during the series. However, it seems to take the form of a crocodile and is connected in some way to the Moon. It's certainly been around as long as Seth and the Dark Ones have and it's probably not good, just antithetically opposed to them. Being its host gives Jessamyn some degree of supernatural invulnerability and some extra super-strength on top of the cybernetic augmentations she already had.
* Seen in ''Literature/PerryRhodan'' once in a while. For a time, the eponymous protagonist himself had "Whisper", an intelligent alien symbiont who could be worn like a cloak and in exchange for regular baths in a protein-rich nutrient fluid endowed his wearer with telepathy and enhanced night vision; for another example, part of the entire ''culture'' of the Duchy of Krandhor was the common use of "spoodies", tiny insectoid creatures that implanted themselves under the host's skin (usually on top of their skull) and provided a measurable intelligence boost.
* A short story titled ''Idiot's Crusade'' has an alien quietly fuse with [[IdiotHero the stupidest kid in town]] to study humans ForScience. A side effect of this is that the boy gets a ''massive'' amount of powers (and total control over them), but without any enhanced intelligence. This leads to a rather disturbing ending, where [[spoiler:the boy, in an effort to make the world "happier", decides to go to the UN building to use his powers to improve the moods of the world leaders (while still lacking the mental capacity to think out the effects or ethics of his actions). Meanwhile, the alien realizes [[AndIMustScream there is no way for him to detach from the human]], meaning the idiot is guaranteed his powers for quite a while.]]
* In ''Literature/{{Pact}}'', after Blake Thorburn invites various local spirits in to fill the gaps in his being, they take the form of [[AnimatedTattoo mobile bird tattoos]] on his arms. He can remove them to send them to do minor tasks for him, such as moving objects or powering SympatheticMagic, but at significant cost to his own metaphysical stability.
* ''[[Literature/AMagesPower A Mage's Power]]'': After a trial in a desert, Eric is given the spirit of Dengel, a legendary mage. He has access to all of Dengel's knowledge which gives him a leg up on older mages. However, he does not have Dengel's spiritual might and so he has to make up the difference with guile.
* The heroes of ''Literature/TheKaneChronicles'' serve as vessels of the Myth/{{Egyptian|Mythology}} gods.
* Nearly all Surgebinders from ''Literature/TheStormlightArchive'' are this. [[spoiler: They get powers from having spren bound to them by having a quality matching the quality that the spren stands for. Kaladin, for example, is an honorable person and thus is bound to an Honorspren. The powers increase as they choose to embody the ideas of their spren, with the spren eventually becoming an extremely powerful living weapon. If they reject that quality or idea, they kill the spren instead.]]
* ''Literature/EdenGreen'' and the sequel ''Literature/NewNight'' portray humans unwillingly infected with an immortal needle parasite, most of whom choose to use its [[BodyHorror horrifying abilities]] to protect others.

[[folder: Live Action TV ]]
* Blending with a symbiote in ''Series/StargateSG1'' can result in this: the human (or other creature) gains greatly increased healing abilities, a near-perfect immune system, and an elongated lifespan. They also get the sum total of all the knowledge of the symbiote. The downside? They have to share their body and mind with another intelligent creature. The Tok'ra believe that equal sharing of the body between symbiote and host is the proper way to do this, and only take unwilling hosts in extreme circumstances. The [[BigBad Goa'uld]] [[PuppeteerParasite do not share such morals]].
* ''Series/KamenRider'' has a couple of examples:
** Ryotaro Nogami, Series/KamenRiderDenO, is ([[HeroicSelfDeprecation by his own admission]]) a NonActionGuy; but as a [[RippleEffectProofMemory Singularity Point]] he can still maintain control of his body even when possessed by Imagin. His [[TheHeart good nature]] and HeroicWillpower are what brings the team together and creates both of Den-O's {{Super Mode}}s, Climax Form (which requires the Imagin to work together as a team) and Liner Form (in which Ryotaro fights on his own without being possessed).
** Haruto Souma, Series/KamenRiderWizard, became a magic-user by resisting his DespairEventHorizon through HeroicWillpower (those who don't are killed and replaced by their own inner Phantoms). Since then, he's made it his mission in life to be the "final hope", preventing others from falling into despair and becoming Phantoms. [[spoiler:When his Phantom was destroyed, he ended up ''bringing it back to life'' in order to protect his friends, and thus created his SuperMode Infinity Style.]] For its part, Haruto's Phantom gradually goes from TeethClenchedTeamwork (since if he dies, so does it) to actually respecting him and being a willing partner.

[[folder: Tabletop Games ]]
* ''TabletopGame/{{Exalted}}'': This is how Infernals are made: a minor demon bearing an Infernal exaltation envelops the body of the Infernal to-be in a chrysalis, as the body and mind of the Infernal adapts to the exaltation. The soul of the demon (designated a 'Coadjutor') is absorbed into the Infernal; it remains sentient (though not always active) and may act as the other voice inside the Infernal's head.

[[folder: Video Games ]]
* ''VideoGame/{{Prototype}}'':
** Alex Mercer survived the Blacklight Virus and got powers from it. [[spoiler: [[SubvertedTrope Or so it seems.]] It turns out it's not that he survived but that the virus ''is'' him. The guy 'hosting' him was also a ''complete bastard'' - so spectacularly evil that the flesh-eating super-virus that ate him was an improvement.]]
** [[VideoGame/{{Prototype 2}} James Heller]], same powers, is also an example; perhaps even a purer one.
* ''Franchise/ShinMegamiTensei'': [[VideoGame/ShinMegamiTenseiIIINocturne Nocturne]] has [[spoiler:Lucifer]] inject the main character with a parasitic demon called a magatama near the start of the game, transforming him into a half-demon.
* ''VideoGame/{{Skullgirls}}'' has a couple of these, most prominently Filia, who plays host to Samson (not the one from Literature/TheBible). She combines her own fighting prowess with Samson's CombatTentacles.
* Sora from ''VideoGame/KingdomHearts'' managed to do this twice: the first is with [[spoiler: Ventus]] at the end of ''VideoGame/KingdomHeartsBirthBySleep'', and again with Roxas in ''VideoGame/KingdomHeartsII'', giving him the ability to [[DualWielding Dual Wield]].
* The spirits in ''VideoGame/ShiningTheHolyArk'' allow our three main heroes to do things mere mortals couldn't possibly do.
%%** And Innovators in the ''Franchise/ShiningSeries'' in general count.
* Jill Valentine in ''VideoGame/ResidentEvil5'', thanks to the anti-bodies in her system from her T-Virus infection in ''VideoGame/ResidentEvil3Nemesis'', is completely immune to the mutagenic effects of the countless viruses that Umbrella has spawned. [[spoiler:Unfortunately, this is also the reason Wesker's MindControl chest-thing worked on her without killing her.]]
* ''VideoGame/ResidentEvil6'' gives us Sherry Birkin and Jake Muller. Sherry still carries the G-Virus in her body from her infection in ''VideoGame/ResidentEvil2'': The vaccine she received stopped her from mutating but gave her a ridiculously sped-up HealingFactor. Jake on the other hand has a variant of the Progenitor Virus in his system which he inherited from dear old dad, which boosts his [[CharlesAtlasSuperPower physical capabilities]] and makes him immune to the C-Virus -- hence his involvement in the plot, as his antibodies are essential to make a C-Virus Vaccine.
* In ''VideoGame/ResidentEvil7Biohazard'', Zoe Baker is infected with the same mutagenic fungus as the rest of her family, but, for whatever reason, she's exempt from the mind-control aspects of it. This allows her to act as Ethan's MissionControl, guiding him towards escaping the Baker plantation.
** [[spoiler: Also, it's heavily implied that Ethan Winters himself became infected early into the game, but lucked out by getting the physical boosting side-effects -- most notably a decent HealingFactor that lets him [[PullingYourselfTogether reattach severed limbs]] -- long before the mind-whammying side-effects started kicking in, allowing him to take down the BigBad.]]
* The Seru from ''VideoGame/LegendOfLegaia'' grant their human host a variety of superhuman powers as part of a mutual fusion, which may include (depending on the Seru) ElementalPowers, SuperStrength, or flight. In the presence of the Mist, however, this turns to DemonicPossession; the main character's Ra-Seru are immune to this downside.

[[folder: Webcomics ]]
* Abbey from ''Webcomic/{{Gnoph}}''. Her powers come from the symbiote Scut, who lives in one of her lungs. Gnoph in general work this way, and are implied to be in common use on Abbey's homeworld.

[[folder: Web Original ]]
* In ''Literature/{{Worm}}'', [[spoiler: every parahuman in existence appears to be an example, as when they get their powers they enter a relationship with a being called a passenger, which gives them access to their powers and makes sure they have the RequiredSecondaryPowers to survive having them.]]

[[folder: Western Animation ]]
* In the ''{{WesternAnimation/Futurama}}'' episode "Parasites Lost", Fry gets infected with worms. These worms make Fry stronger, smarter, and healthier. The Planet Express crew [[FantasticVoyagePlot travel into Fry's body to get rid of the parasites]], then Leela stops them because she likes the new Fry better. [[StatusQuoIsGod And then Fry removes the parasites anyway]] because he wants to know that Leela likes ''him'' and not what the parasites made him into.
* In ''[[WesternAnimation/MenInBlack MIB: The Series]]'', when a Symbiote attaches to you the upside is nigh immortality via healing/rejuvenation, rubberman-like expansion tied to an epic shapeshifter baggage, varying amounts of shapeshifting for yourself, on and off again ability to breathe fire, and a "lay on hands"-ish ability to heal others. the downsides, however, are that you could get attached to an annoying Symbiote and you have 20 hours before you [[IdentityAbsorption merge]] [[FusionDance permanently]].
* [[TheChosenOne Avatars]] in ''WesternAnimation/AvatarTheLastAirbender'' and ''WesternAnimation/TheLegendOfKorra'' serve as earthly vessels of Raava the Avatar Spirit, who enables her hosts to channel her (along with the spirits of her former hosts) and harness ElementalPowers.

[[folder: Real Life ]]
* One theory of the origin of mitochondria. The cellular powerplant organelles have their own DNA separate from the nuclear DNA, and it is similar to some bacterial DNA. It's theorized that these proto-bacteria had superior biochemical processes when it came to metabolism, and in exchange for some form of mutualistic symbiosis, linked with other proto-life that had much bigger cells. They became so intertwined as life evolved that these bacteria just became another part of the cell.