->''"There's this really cool OC that pops up in a lot of [[Literature/HarryPotter HP]] fics. He's suave, snarky, handsome, a bit of a git, but super good-looking. For some reason, people keep calling him Draco Malfoy."''
-->-- ''Fanfic/SeventhHorcrux''

In {{fanfiction}}, it's very common for favoritism to show up. After all, everybody has their preferences and [[DracoInLeatherPants regardless]] of their [[EnsembleDarkhorse role]] in the story, it's never a uniform thing. However, one frequent thing is for the author of a particular fanfic to appropriate a character. Rather than creating an original character, this author will overhaul the role, importance and personality of a particular canon character they like in order to make the character "ideal" (i.e., a stereotypical MarySue).

Every canon character in fanfiction represents the fan's re-interpretation of that character. They aren't the original author, so they don't have first-hand knowledge of the inner mechanics beyond what is shown in the released materials. The most they can do is try their best to emulate that character using the information they have, with varying levels of success. This trope refers to the more extreme situation, when a character's most basic, undeniable traits are flat out ignored in favor of the author's own views and/or desires. For example, a fanfic of a HaremAnime that takes the ShrinkingViolet character and has her all of the sudden grow a backbone and force her way into being the official romantic interest of the hero, or that turns the hero from an ordinary AudienceSurrogate into a hyper-charismatic badass who is [[TheCasanova instantly able to woo any woman in seconds]], would definitely be a case of this trope. In short, it's as if a spirit (the author) [[DemonicPossession possessed their bodies]] and took over to create a '''Possession Sue'''.

Usually, it's secondary characters that get this treatment, but it's not unheard of for main characters as well. For example, if a fanfic of ''WesternAnimation/InspectorGadget'' has the title character all of a sudden gain a near-omniscient level of detective expertise (hell, even just half-decent detective skills) and singlehandedly expose and arrest all of Dr. Claw's organization, ''without'' this being somehow subverted at the end and/or played for laughs, that would definitely be a case of this.

The traits that mark a Possession Sue are just as myriad as the ones that mark a regular old MarySue. As a general trend, authors that make these characters also tend to strip away much of the original characterization in the process of "idealizing" their favorite character. They might [[InstantExpert be made uber-competent]], [[BeautifulAllAlong turn out to be extremely beautiful after all]], [[AlwaysSomeoneBetter outshine every other character]], [[StrongAsTheyNeedToBe gain new and previously unknown powers]], have a revelation of being someone's [[LukeIAmYourFather long-lost child]] and what-have-you from the CommonMarySueTraits. Other times, they're rewritten to resemble the original author more closely, such as having a similar family situation, or having identical tastes in fashion and music. Most importantly, though, is that the character is favored by the author to such a point that the same MarySue favoritism present in other characters and the universe come up.

As far as the MarySue subtypes go, any of them can apply, but the single most common is FixerSue. After all, the author is pretty much applying their own viewpoint on how the canon ''should'' go and hijacking a character to "fix" it is probably the single biggest inspiration for rewriting a character. Otherwise, the author might just be trying to avoid the stigma of original characters while still wanting a mask to wear as they insert themselves within the story.

The term most often used for this is actually "Canon Sue," but there's a second, different (if related) trope also known as CanonSue. Where a CanonSue is a canonical character that has Mary Sue traits in the original work, a Possession Sue is a canonical character that is ''given'' Mary Sue traits in a fanwork. When canon writers forcibly turn their own characters into Mary Sues, Possession Sue-style, it's a form of CharacterDerailment. Often overlaps with SelfInsertFic.

Compare with the OCStandIn, which is not necessarily a Sue, but does share the characteristic of being a canon character--in this case, an underdeveloped FlatCharacter--overhauled to an author's liking.

Contrast CopyCatSue, which, rather than stripping the characterization of a canon character to make them "more appealing", instead synthesizes a blatant clone of a canon character.
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!Please do not add examples to work pages, this merely [[Administrivia/DefinitionOnlyPages defines the term]]. %%https://tvtropes.org/pmwiki/posts.php?discussion=1596363404091310800