Fixer Sue

Amongst Fan Fiction writers, the Fix Fic is incredibly popular due to everybody having an opinion on how a particular canon should go. Don't like how they took your favorite character and Dropped a Bridge on Him? Nah, He's Just Hiding. Your One True Pairing got ruined? Derail a few characters to get things on the right track. Wish the villain wasn't such a cad? Maybe he found that there was good in his heart after all. But how are you going to make this happen? This is when you call your local Fan Fiction repair business and request they send out a Fixer Sue.

The Fixer Sue is a unique entity in the Mary Sue class in that he or she was never meant as a character so much as a plot device. They may or may not represent the author or indulge in the Common Mary Sue Traits, but what they do is use their magical plot altering powers to get things "back on track" in the eyes of the author. The plot still elevates the character to unrealistic heights, but instead of it being done for the greater glory of the author, it's to get to a particular end within the canon. Once the character is done fixing all the "problems", he or she will usually get unceremoniously removed (either by death, being Put on a Bus, or just getting downgraded to a minor character).

Fixer Sue can be just anything and everything so long as he or she gets the results desired. A Villain Sue comes in and ceremoniously kill off the Love Dodecahedron outside of the One True Pairing? Hey, that works. A Sympathetic Sue wangsts about how her (non)canon sister is depressed and unloved, inspiring the protagonist to choose her instead? That also works. This is also often done in a tongue-in-cheek manner (for example, a Purity Sue shows up and makes the hero realize how much he really hates extremely girly women and goes for the tomboyish childhood friend).

This can still happen within a canon itself, but it's quite rare. Still, maybe the author just ended up hating a particular path that was taken and decides to go head over heels during the Author's Saving Throw. Alternatively, the character might just exist as a walking Deus Ex Machina and the story surrounding him or her is based around "fixing" every perceived social wrong. Characters prone to this include the Blithe Spirit, the Magical Negro and The Drifter Walking the Earth.

Somewhat more believably, this may be combined with Peggy Sue (not a Mary Sue type, by the way), in which a canon character does this as a part of Setting Right What Once Went Wrong, or even as an unexpected coincidence or consequence of their actions.

Anime and Manga

 * There are a high number of Sailor Moon fanfics that try to remove the canon lesbianism of Haruka and Michiru. Most of them just turn Haruka into an evil butch pervert who abuses Michiru and create a dashing Gary Stu to make Michiru heterosexual. The most infamous example, however, was cooked up by the notorious Save Our Sailors website, which actually used Haruka as the Fixer Sue and tried to pass it off as canon. Their story claimed that there was a Prince of Uranus in the past that was Sailor Uranus' brother and Michiru's past lover, whom Sailor Uranus passed her powers onto when she died and caused him to be reincarnated as a woman that still loved Michiru. Therefore it wasn't really homosexuality because Haruka was really a boy. Cue Internet Backdraft and loss of what little credibility they ever had! (Naoko Takeuchi has gone on record saying that Haruka is not and never has been a man, but when has that stopped anyone?)
 * The long-dead Queen Serenity gets used like this a lot in Sailor Moon fics. Her powers will be boosted from being simply powerful to being capable of nothing short of divine miracles, then, because she's dead, she will poof away once her job is done and the author doesn't have to even come up for a plausible exit for her. Because Queen Serenity is such a legendary figure in the canon, all the characters will accept whatever she did as correct, even if the fix applied is something that would have appalled them in canon. Like say... a fix fic that tried to correct Haruka and Michiru by having Queen Serenity appear and "correct" Haruka's gender to male, which is regarded positively by everyone involved.
 * The Neon Genesis Evangelion fanfic "Higher Learning" stars Kaoru Miyazaki, a Kid From the Future Fixer Sue masquerading as a teacher for the main characters. Watch as he thwarts the nefarious plans of the The Omniscient Council of Vagueness and the Magnificent Bastard, heals the severe psychological problems of the teen heroes and seduce their Bunny Ears Lawyer caretaker; and marvel at the enormous popularity this fic had with the Mary Sue-hating crowd back when the Evangelion fandom was alive!  Though, admittedly, the fic was still quite good when compared to other Fixer Sue fics.
 * Shioshiro Himiya, from the Weiss Kreuz fanfic Kind des Schicksals, is another Kid From the Future Stu - the child of Aya Fujimiya and Ken Hidaka, both of whom are male and don't like each other much - who conveniently knows the entire plotline and comes back in time to save Weiss and Schwarz from the evils of Weiss Kreuz Gluhen. His presence is the answer to just about every issue the characters have, no matter how deep-rooted, and once his purpose - to warp the story into a Fan Girl-approved shape and get fan-favorite pairings to hook up Because Destiny Says So - is fulfilled, he conveniently dies. This fic is also absurdly popular. Though one wonders if it would be as popular if Shioshiro had been 1) a girl and 2) someone else's child.
 * Pretty much every Original Character or Ascended Extra in Cori Falls's Pokémon fanfiction exists solely to make sure everyone knows how perfect and special her version of Jessie, James and Meowth are and that Ash Ketchum is stripped of any positive qualities to prove what a Complete Monster he "really" is.
 * The School Days short fanfiction The Guardian Angel is a non-Egregious version of this, but it is kinda a Mary Sue Classic and a Pair the Spares fic. Haiko Nai is an 18-year-old trained-from-childhood bodyguard (but otherwise completely normal) hired by a unknown client to protect Sekai, Kotonoha, and Makoto. The plot's rather vague in regard as to who the client is or Haiko's backstory. Anyway, he infiltrates the school, after a few mishaps quickly becomes friends with them (due to a Running Gag involving sandwiches), saves Sekai from a drunk driver and thus earning school-wide fame, sheepishly suggests that Kotonoha take Taisuke to the festival (whereupon Taisuke immediately confesses his love to her), and forms a close relationship with Setsuna. When Sekai storms off after finding out Makoto was cheating on her, he follows and gets stabbed trying to stop her from killing Makoto. He goes into a coma from blood loss, and wakes up three months later right after being pronounced effectively dead, much to the utter joy of his new friends. Predictably, they lived Happily Ever After.
 * In many Ranma ½ fanfics, Ranma Saotome is made into a Fixer Sue of sorts. This would make sense since probabilities would become warped and wild things would occur whenever he's around.
 * It's not uncommon in Ranma ½ fics for Ranma to have an unknown cousin, brother, uncle or ancestor who suddenly appears and solves all of his problems.
 * On the other side, the entire length of canon couldn't solve Ranma ½'s Love Dodecahedron, but one mediocre fight with a Fixer Sue collapses the whole thing, quickly and neatly. A great number of fics start off with one of the girls in mortal peril from some new enemy, and it is only after he rescues her that Ranma finally realizes how important she really is to him. Then the majority of the story is actually spent tying off all the romantic loose ends.
 * Parodied in Otaku Three - EVA Revolution by Jared "Skysaber" Ornstead, where his dangerously genre savvy Marty Stu tries to derail Neon Genesis Evangelion not through sheer badassitude or Xanatos Speed Chess, but instead by feigning Wrong Genre Savvy until he turns the series into a Super Robot show. Hilarity Ensues.
 * As in Ranma fics, Love Hina has many involving Keitaro suddenly having a brother or cousin who shows up to fix the story.

Film

 * There are Rocky Horror Picture Show fanfics out there that feature a fan-character (often a female) bringing Dr. Frank N Furter back from the dead and/or simply going back in time to prevent him from being killed in the first place.
 * Another common sort of Rocky Horror fic is essentially the Fixer Sue in reverse; the character in question is Frank's good heterosexual lover from back home on Transsexual, who invariably dies tragically, causing Frank to snap and become a bisexual transvestite. The Unfortunate Implications of this are oft pointed out by sporkers.
 * Just about half of all Newsies fics ever written involve a girl who watches Newsies and then time-travels back to 1899 via a "magic paper", and uses her knowledge of the plot to remove Sarah from the storyline and hook Jack and David up (or just hook up with one of the newsies herself).
 * The Seven Percent Solution by Nicholas Meyer is a Sherlock Holmes fic bizarrely combining this with using an historical character as Possession Sue. You see, actually Sherlock Holmes was just a delusional junkie. And the one desperately needed there is all-shiny... who? Yes, just like that.
 * It's common in fics based on the film version of The League of Extraordinary Gentlemen to introduce a female OC, whose purpose is either to facilitate a slash pairing between two of the guys or to hook up herself with whichever of the team the author found most attractive. Or both.

Literature

 * The number of Harmonian-written Harry Potter fanfic that feature an adult Harry going back in time to "fix things." These are mainly things like hooking Harry up with Hermione (who gets derailed into a Purity Sue who can do no wrong even if she acts like a bitch) and making sure that Ginny Weasley (a character more hated than Voldemort among Harmonian circles) is revealed to be the conniving untrustworthy back-stabbing psycho-bitch that the Harmonian community wishes J. K. Rowling had written her to be.
 * Not to mention the kind of crap that gets inflicted on Ron.
 * Ebony Dark'ness Dementia Raven Way takes this to Reality Warping levels.
 * So does The Girl Who Lived series, where "Rose Potter" fixes tons of "problems" with the original: capturing Peter Pettigrew, "punishing" Ron for being a teenage boy and later Ginny for getting in the Harmonian way... I mean, being mean to Fleur, fixing Hagrid's fashion sense and Hermione's rampant SPEW promoting, Cedric's death... and basically this list could go on forever.
 * The amusing thing about Rose Potter is that she's an unintentional subversion; given how massively overpowered she is, Rose ought to be able to solve all the Wizarding World's problems in no time flat, but events still unfold pretty much the same way they did in the books. Harry was only human. What's Rose's excuse?
 * Gertrude "Danger" Granger is directly or indirectly responsible for, , , , , ...and all that is just in Living With Danger. There's a reason the series as a whole is called the "Dangerverse".

Live-Action TV

 * There are dozens of iCarly fics for the Sam/Freddie Belligerent Sexual Tension styled Seddie ship, where a Fixer Sue shows up as a long-lost sister or cousin of Freddie, and immediately helps Sam and Freddie hook up.
 * iCarly's Father has Col. Shay as a Fixer Sue. However, this is a case of Tropes Are Not Bad, because iCarly is set in a Crap Saccharine World, most of the characters are various forms of Jerkass. It all gets Deconstructed by Col. Shay. All the characters equally get what's coming to them but not in a heavy handed and without making it a Revenge Fic.
 * A good number of Rose shippers in the Doctor Who fandom use Bad Wolf as a frequent Fixer Sue to get her back with the Doctor.
 * And Lets Not Forget that Doctor Who Crossover Manga which uses Crossovers to insert an older sister to the Elric Family embedded with Ideya Tattoos that somehow Flings them beyond the gate and makes their Mother the first successful human Transmutation But when she tries to pull them back home her right arm becomes the Eldritch Abomination we've come to know and love. Ed's More or Less the Same, Al left behind a hand and a foot... and Ed Tethers the Now Non-Existant Soul of Timmy Turner to the familiar Armor in the Corner
 * A truly terrible Fix Fic of the American The Office written somewhere around season 3 features Jim's "best friend" who promptly shows up and hangs around the office for no reason other then to fix everyone's problems. Naturally she gets Jim and Pam, and all the other couples, together. And when she started calling out Michael and Dwight on their character flaws, she started taking away things that made the comedy series funny!
 * There is a certain Buffy the Vampire Slayer fanfic out there which cranks this trope to the highest level. A woman from the "real world" pretty much descends like an angel from heaven into the Magic Box and proceeds to spend chapter upon chapter spouting off about how wonderful Spike is, making him out to be the sweetest, most courageous boy ever and verbally tearing down anyone who stands in the way of this new worldview. (And the Spike/Buffy ship.) This, of course, means that Riley and Angel are revealed as a speciesist sociopath and a vicious, egotistical pedophile, respectively. The Fixer Sue flat out says that she hates Riley and thinks he's boring, but gets a thin guise of "trying to help Angel"... for about three minutes, before listing every way he's terrible. (A majority of these reasons are blown way, way out of proportion or just made up "psychological" analysis.) They are exiled by the "enlightened" Scoobies, who may have ripped them apart with their bare hands if the author had deemed it fitting drama. It gets worse after that.
 * Heroes: Arthur Petrelli seems to be a canon version, as he took away Peter's endless supply of powers and also managed to get rid of the hated Maya.

Video Games

 * Star Fox usually has either Falco or Wolf be Fixer Sues in order to "rescue" Fox from Krystal. Strangely enough, another rising example is the ret-conned Miyu, a female lynx, from Star Fox 2. This troper can think of two fanfics (by the same author, no less) where Miyu "saves" Fox from an abusive-ized Krystal; one of them even has her express belief that, though he's a fox and she's a lynx, they can reproduce and have children, even though they're two entirely different species.
 * This also works in reverse: Fox himself becomes a Fixer in order to get Krystal back from Panther, who is attracted to her. Expect Panther to be demonized as a womanizer and a rapist, even though when he does get together with Krystal in Star Fox Command, he is rather devoted to her, or at least is respectable towards her, the same of which cannot be said for Fox in the same game, who openly neglects her.
 * A lot of Fate/stay night fanfics will introduce a Fixer Sue or turn an already existing character into one in order to save Sakura. It doesn't do much for the quality of the fics, or fan opinion on Sakura in general.

Western Animation

 * In the Metalocalypse fanfic New Roommate, Alexis Ofdensen (yeah, she's his daughter; you can see where this is going) overlaps quite a few Sue types, but at her core is a Fixer Sue. The author's notes suggest that the character and story were created in order to counteract the number of Dethklok slash stories and art already published. She exists mainly to have nice, heterosexual sex with every member of the band in order to counterbalance the perceived Ho Yay within the series.
 * Well, hey, it worked whenever they were shown having sex with women in the show, right?
 * In the otherwise good Invader Zim fic (it was on the Fanfic Recs!) Invader Zim: The Series, original character Nick is said to be a Fixer Sue (by Johnny the Homicidal Maniac, to be exact). It should be noted that  his efforts were unsuccessful, and while he makes friends with most of the canon characters, he also gets his fair share of crap dumped on him too.
 * Any time Bass is featured in a Ruby-Spears Mega Man fic, there's a good chance he'll be one of these; his primary purpose is to make Proto Man leave Wily (for whatever reason the author sees fit) and force the cartoon to be a different-looking Capcom-Mega Man. Then he tends to drop off the face of the Earth. Arg.