Alternate Universe

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Tropes and genres
Synonym(s)AU, Alternative Reality, Altiverse, Alternate Reality, Alternate Timeline, Alterniverse
Related tropes/genresUber, Canon AU, fusion, pastiche, constructed reality, crossover, Mirror Universe, What If
See alsoOriginal Universe, Shared Universe
Related articles on Fanlore.
You may be looking for Star Trek zine Alternate Universe 4.

Alternate Universe (often abbreviated as "AU") is a descriptor used to characterize fanworks which change one or more elements of the source work's canon. Broadly, an AU may transplant a given source work's characters to a radically different setting, shift the genre in which their adventures occur, and/or alter one or more of their professions, goals, or backstories.

AU fanworks cover a great deal of creative territory, and much discussion has gone into how exact to classify the term and its subtropes. The openness of AUs allows fans to stretch themselves creatively.

The term AU covers a wide range of divergence from the original canon, from universes where only a tiny tweak has occurred to diverge it from the canon to AUs that are so different as to border on origfic - sometimes called "radical AUs". Some fans question the merits of calling these works fanfiction, arguing that they are so unrecognisable as to be effectively original. Another argument is that all fanworks are by their nature AUs, as they will inevitably differ from the canon in some way, shape or form.


The term most often refers to fanfic, but fanart can also invoke AU tropes – for example, steampunk versions of universes.

AU-type stories are common in Japanese doujinshi as well, often featuring characters recast as high school students or animals. Some animanga canons include AUs as well. Constructed reality, a term used in Vidding, is essentially the visual counterpart to AUs in written fanfic.

AU fanworks cover a great deal of broadly defined creative territory with many subtropes. Under the broad umbrella of "alternate universe", one can find both fanworks that only diverge from their source canons in a single, specific way (for example, a Star Wars AU in which the first Death Star is not destroyed) and fanworks that have changed things so significantly the characters are almost unrecognizable without their names (which is sometimes when an author will file off the serial numbers).

Fans use AUs to stretch themselves creatively and to engage in flights of fancy. They may also serve to promote fandoms with small canons, to present the writer's views regarding canon-related controversies, and/or to provide social commentary related either to the source canon or to some aspect of the AU being presented.

It's generally agreed that the most effective AUs are those in which—even in the most radically changed circumstances—the transplanted characters are clearly recognizable in relation to their canonical counterparts. However, there is much controversy in fandom as to what makes such characters recognizable and precisely when an AU deviates so far from canon that it effectively becomes original fiction—at which point it may no longer be considered "proper" fanfic, and may no longer appeal to fan audiences.[1][2][3]

Definitions and Categorizations

Fortunately for purposes of classification, a large proportion of AU fanworks fall into recognizable and somewhat popular subgroups.

Canon AU

"Canon AU" has two common definitions:

  1. an AU that originates within the commercial source work itself.
  2. a fanwork AU that diverges relatively narrowly from that of its source work.

Fanworks based on source-canon AUs may be labeled in various ways as well, sometimes using source-canon episode titles, and sometimes coining new terms. In Stargate Atlantis fandom, Mensaverse or Mensa AU denotes works spun off from the episode "McKay and Mrs. Miller", while in Xena fandom, Conqueror tags stories set in the world of the Hercules episode "Armageddon Now".


Fusions—works in which two (or more) fictional universes are condensed into one—are sometimes considered a special case of AU; more often, they're considered a subtype of their own, standing between AUs and crossovers.

Mirror Universe

A mirror universe is a type of alternate universe in which familiar characters are given reversed characteristics. Heroes might be evil, or at least far more ruthless and aggressive. This is often indicated visually by more sexually revealing clothes, longer hair and/or facial hair, or quasi-fascist imagery.

The term originates from Star Trek, which has several episodes portraying a canonical alternate universe in which the peaceful Federation never existed, replaced by the brutal, conquering Terran Empire. The first "Mirror Universe" episode was the TOS episode Mirror, Mirror. [4] [5]

In general when a fanwork is stated to be set in a 'mirror universe,' it means the story will be darkfic. The canonical "moral inversion" of the Mirror Universe setting gives the fanwork creator the opportunity to depict dark subjects that would not be part of canon. Characters from the regular universe and the Mirror Universe may also interact, giving the writer an opportunity to explore doppelganger or Evil Twin scenarios.


While the Hollywood-coined term "reboot"—popularized in connection with Star Trek XI (2009), which went to great lengths[6] to characterize itself as existing in a parallel timeline to that of Star Trek: The Original Series—often arguably describes an AU version of a previous source work, fandom has not generally adopted the term either as a descriptor for fanworks or of the fandoms arising from commercial reboots.

Shared Universe

In some cases, an AU fanwork can become popular enough that its readers are inspired to create additional works in the same setting. This can result in a "shared universe" consisting of anywhere from a handful of stories to hundreds. (This usage of the phrase differs somewhat from that of professional writers working in "shared world" settings such as the Wild Cards, 1632 or Thieves' World books.)


Uber is a popular fanfic genre in the Xenaverse. The trend was prompted by a Canon AU in the episode "The Xena Scrolls."

An Uber-Xena story takes the essence of the characters and places them in an AU.[7], but the uber characters do not have the same names and appearances of the canon characters. Sometimes they are descendants or reincarnations. Usually they resemble the originals physically, and they share the same type of bond.

Universe Alteration

UAs are very similar to AUs, but instead mean "Universe Alterations". Unlike canon divergence, UAs are set in the canon universe, but with "alterations", as the name suggests. For example, a character is born younger, certain things exist in an otherwise-unchanged universe, etc. This type of AU can sometimes be considered synonymous with canon AU or canon divergent AU.

Other Classifications

Categorizing AUs is complicated by the fact that over time, different naming conventions have been used by different fandoms and fan groups. For example, some fans use alternate reality to describe stories that diverge from source canon at a specific point, while others use the same phrase to describe stories that drop characters from their source canons into an entirely different milieu. Likewise, the 1990s saw an effort made to adopt "extended universe" to describe narrowly divergent stories and to limit "AU" to describing more radically divergent works. (Not surprisingly, it didn't take.)

One taxonomy of AUs popularized by yourlibrarian the post What's In An AU? in 2010 includes:

  • AC - alternate characterization
  • AL - alternate life
  • AS - alternate setting
  • AT - alternate timeline

Another taxonomy[8] discussed differences between types of fanworks characterized as AUs or ARs especially pertaining to canons that themselves already include alternate realities and alternate timelines, such as Stargate and Star Trek, distinguishing between fanworks set in:

  • AR - alternate reality, such as ones shown in various episodes of Stargate, Star Trek, and other shows (e.g. Mirrorverse, Mensaverse, Supernatural's The French Mistake verse). (Closely related to the canon reality and canonically crossing over with the canon reality.)
  • AT - alternate timeline, such as ones shown in the SG-1 episode Moebius and in the reboot Star Trek film. (Canonic offshoots created by manipulating the timeline of the prime canon reality.)
  • AU - alternate universe. (Not referenced in canon, purely transformative works that widely diverge from canon with alternate settings for the canon characters.)

Canonical Use

The concept of AUs is not restricted to fanworks. Time Travel in fiction often involves travel through or the creation of alternate universes (sometimes called "alternate timelines"), although many canons have a canonical alternate universes without the any time travel. An early example — and a common trope — is the movie It's a Wonderful Life (1949) and the short story it was based on, The Greatest Gift by Philip Van Doren Stern (written in 1939), in which an angel shows the main character what life would be like for his loved ones if he had never been born.

Star Trek: The Original Series brought the concept of alternate universes to much of the American public, most notably with the episode Mirror, Mirror: the Mirror Universe, a type of alternate universe in which familiar characters are given reversed characteristics, has featured heavily in extended canon materials and recently has become very important in Star Trek: Discovery. Other notable TV Western TV shows with alternate universes include Xena: Warrior Princess (1995),[note 1] Buffy the Vampire Slayer (1997),[note 2] Red Dwarf (1988),[note 3] and Supernatural (2005).[note 4] Western comics publishers are also known for alternate universes: DC has Elseworlds[note 5] and Marvel as What If...?).

Alternate universes are also popular in Eastern media. The One Piece anime has several specials which portray the cast as superheroes and supervillains, or denizens of a Tokugawa-era Japanese town. Kazuya Minekura wrote Executive Committee, a silly high school AU of her manga Wild Adapter. Puella Magi Madoka Magica involves magical girls repeating increasingly dark iterations of the same timeline. Other notable examples include Dragonball Z (1989),[note 6] the 2003 Fullmetal Alchemist anime,[note 7] Tengen Toppa Gurren Lagann: Parallel Works (2008), and Tsubasa: Reservoir Chronicle (2003).[note 8]

Examples of AU Subtypes

While AUs exist in nearly infinite variety, a high proportion can be grouped into recognizable subtypes, with examples that can be found in a variety of fandoms. Among these are:

Character-Type AUs

Period-Based AUs

Setting-Specific AUs


Comments by Fans


Why do AUs, so many of them just seem like they were written to get the guys in different costumes. I firmly believe in fun role-playing, and fantasizing about what B and D would be like in a Victorian London setting seems like perfectly harmless fun to me. Obviously, as I said, it requires some work to make them recognizable and to make the plot interesting. I see the point of an AU to be having events happen that couldn't happen in the standard CI5 or Federation setting.

And for all those republicans out there who say "but I LIKE the CI5 universe" or "the Federation is so cool", ask yourselves how often do slash stories ever really use the original universe to good effect? Stories that get the lads to a cabin in the woods, away from their standard setting, are propping up my bookcases by the zillions. At least when someone scribbles an AU, there is some energy and thought going into setting and plot, rather than just "who gets the bed, heh heh," and "the heat doesn't seem to be working, fancy that."

– comment by Lynn C at Virgule-L (quoted with permission), October 9, 1993


...AUs seem to proliferate mainly in single-pairing fandoms — probably out of boredom. The possibilities of any relationship are exhausted eventually; the novelty wears off and the honeymoon's over. In shows with ensemble casts, like B7, fans move on to alternate pairings to alleviate such ennui. This strategy is unsatisfying when the show has a very limited cast, like Pros. (Though they tried, as evidenced by the extraordinary elevation of Murphy, a spear-carrier if ever there was one!) Thus fans move on to AUs, rather like a long-married couple trying to spice up their love-life by doing it in an elevator or while dressed up as pirates.

– from Strange Bedfellows APA #5 (May 1994)

Actually, I rather enjoy a/u's, at least in theory, although [ Alexfandra ] does point out the many, many unfortunate possibilities for tedious bypaths. Some of us don't mind elves (when the writer remembers that elves are an immortal, inhuman, wittily sardonic, goddamn dangerous race, or at least vaguely alien to CI5); archaic language (you're talking about the Shakespeare and Congreve I love); and professions other than hired state killers. They only suck because they're so hard to write and more fans are ambitious than have good sense. The opposite combination wouldn't have led to fandom at all, so we may be ahead, on balance. When a familiar media character (or pair) is put into a nice new setting — historical, fantastical, pastorical, music-comical, whatever, and retains significant aspects of his (or their) original, recognizable, why-we-love-them personality, that's a kick. But it's harder, not easier, to maintain Hutch as a vampire or Blake as a successful revolutionary without losing sight of what made him fascinating in the first place. So finding or writing a story that answers the question: "What, other than UNCLE and cold-war prime-time TV, would make Illya like Illya?" or "How would Illya change and how be the same, in a different world?" is no mean feat.

– from Strange Bedfellows APA #5 (May 1994)


I like a particular show for more than just the characters. I'm interested in the setting; the ethos of the world; the way the characters fit into their places in it. No matter how good the characters themselves are, if that's all there is to a show, I'm not going to be going back there.

Of course, that brings up the fact that characters are a part of their environment. What has happened to them plays an inevitable part in the 'person' they are. Take Obi-Wan out of the Star Wars universe, plonk him in modern-day Manchester, and you've either got an entirely different personality or a completely unrealistic character. [...] A character is so strongly influenced by their environment that if you take them out of it, they are simply people with the same physical appearance but entirely different personalities

[...] When it reaches this point, I start wondering why the author insists on labelling their work as 'fanfic' when there is so little of the original still remaining. Is this an attempt to reach an audience? There are hundreds of slashfic mailing lists out there. By posting to one or more of them, you're pretty much guaranteed that somebody, somewhere, will read your story. Maybe they'll even email you to say, "Hey, kewl story!!!!" By contrast, try finding a place to post your original homo-erotic fiction. It ain't easy, is it?

So, what situation does a writer have to be in to make the answer a radical AU?

Alternative Ain't Necessarily Good by Lena W. Jones


A 2005-or-earlier fan comment about the difference between Ubers in Buffy the Vampire Slayer fandom and AUs. The definition the commenter gives of AUs is what many fans would identify as a canon divergence AU.

AU (Alternate Universe) fiction generally supposes that the regular background of the characters occurs up to a certain point, where the story's background then diverges from the original - for example, Buffy fiction in which Buffy was not raised from death after the end of season five, or in which Tara was not killed at the end of season six (I'm quite partial to the latter idea).

Uber fiction is fiction in which only the natures of the characters are retained. The characters may have lived lives completely different to those of their original setting, but (due largely to the indulgence of authors) their personalities are unchanged. Uber is a sub-genre of AU, with particular requirements.[9]


Today I was reminded of a conversation I was having with someone over the question of "is all fanfiction AU?" The answer to me seemed to obviously be "yes" in the sense that nearly all fanfic is going to deviate from canon in some way, if not now then by being Jossed in the future. There is certainly a good chunk of gen that fits neatly into open canon spaces, but I think the majority of fic indeed skews away from canon in either its premise or in the repercussions for events in the fic.

But my bigger issue is with the term "AU" because it's used frequently to mean what I consider to be vastly different things. I find the term always has relevance in indicating that the story is somehow non-canon-compliant. However, the ways in which this lack of compliance occurs may relate to settings, life histories, character development, or timeline changes. And in some cases the term is used mostly to distinguish cloaked original fic from canon-inspired stories. Moreover, the fandom in which the term is used may affect the definition in ways that are not the same across the board.

For starters, the sort of fic that gets written in the fandom and the laws of its Verse affect the meaningfulness of the "AU" term. "Alternate Universe" is often nothing of the kind. [...]


To reiterate, rather than the blanket term "AU", I think we also need alternate life (AL), alternate setting (AS), alternate timeline (AT), and alternate characterization (AC) if we really want to be on the same page in discussing how fanfic deviates from canon, and when it has nothing to do with canon at all. It's also useful if we want to look at how differently fans can explore different canons.

What's In An AU? by yourlibrarian


From reddit r/fanfiction thread AU tropes - love them or hate them?[10]:

I tend to prefer canon divergence AUs to the ones that take the characters and throw them in completely different set of circumstances, because at that point it kind of feels like, why not just switch the names and publish it as original fic?

I absolutely love the basic AU tropes provided that they're written well. Regardless of whatever show, movie, etc. I'm currently into, I'm always way more interested in the characters over the plots, so putting these beloved characters into different settings and really delving into who they are is right up my alley.

I seem to prefer AU fics when the show is particularly heavy, like Madoka Magica or Evangelion. Seeing characters I care about that had crap relentlessly piled on them find friendship, love, and happiness is nice.


If I had a magic wand to wave at the AO3 tag-wrangling system, the very first thing I’d do is create a supertag for setting/universe alterations that doesn’t include canon-divergence AUs, which are a separate beast.

– shinelikethunder, Partial List of Supertags for the AO3 “Exclude” Filter [11]


I was just thinking about how adorable it is that humans write au fanfiction. Like: Wow I love these two characters and their relationship so much so;

Let them fall in love as mermaids, as spies, as pirates and vampires, in space, in medieval times, in a zombie apocalypse, as hockey players and figure skaters, at a flower shop or coffee shop, the list could go on forever

I like to think of fanfiction collectively as a multiverse where all of these stories happen and they fall in love over and over again in many different lifetimes because I’m a sap like that

Okay that’s all[12]








Notes & References


  1. ^ Xena: Warrior Princess has the "Uber" genre, prompted by the Canon AU of Mel and Janice in the episode "The Xena Scrolls".
  2. ^ Buffy had Wishverse, an alternative reality in which Buffy Summers never came to Sunnydale, and also "the universe without shrimp".
  3. ^ In Red Dwarf they visit a parallel universe, where the characters encountered female versions of themselves. Lister discovers that mpreg is also canon in that universe, when he becomes pregnant by his female counterpart. See the Wikipedia page with plot synopsis
  4. ^ Supernatural has episodes in which supernatural creatures put Dean and Sam in various alternate universes, including one where they're swapped with actors Jensen Ackles and Jared Padalecki).
  5. ^ Also, The Flash and other DC Comics characters who possess super speed and a strong enough access to the speed force have the ability to travel through time or to alternate universes. Flashpoint is a DC comics crossover story arc about an altered DC Universe in which only Barry Allen seems to be aware of significant differences between the regular timeline and the altered one, revealed to have been caused by the history-shattering effect of Barry's attempts to change history. The Flash (2014) has multiple storylines involving travel to alternate universes.
  6. ^ In Dragonball Z, Trunks' time travel in the Cell Saga involves creating alternate universes via creating alternate timelines, although that's not the only canonical example of alternate universes in DBZ.
  7. ^ The 2003 Fullmetal Alchemist anime differs wildly from the manga and the later anime, Fullmetal Alchemist:Brotherhood. In the 2003 version, everyone has an alternate self that lives in our universe.
  8. ^ The characters in Tsubasa: Reservoir Chronicle cross many universes together and are not all from the same universe. The main characters Syaoran and Sakura are alternate universe characters of two characters with the same names from Card Captor Sakura, an earlier CLAMP work.


  1. ^ Lena W. Jones. Alternative Ain't Necessarily Good. Posted 9 July 2000. (Accessed 2 October 2008)
  2. ^ RatCreature. How to construct Alternate Universes that work as fanfic. Posted January 2001. (Accessed 2 October 2008)
  3. ^ James Walkswithwind. The AUness of it All. Posted 4 February 2003. (Accessed 2 October 2008)
  4. ^ Memory Alpha link
  5. ^ Wikipedia link
  6. ^ "Interview with Star Trek XI writer Bob Orci". Archived from the original on 2022-06-08.
  7. ^ Lunacy. Lunacy's Fan Fiction Reviews - Definitions. (Accessed 6 October 2008)
  8. ^ which I'm having trouble finding again, will continue to hunt
  9. ^ Through the Looking Glass (archived link) a Willow/Tara Uber Fanfiction archive, FAQ page, accessed 12 Jan 2022.
  10. ^ May 16, 2016
  11. ^ Partial List of Supertags for the AO3 “Exclude” Filter, July 6th, 2018. (archive)
  12. ^ Tumblr post by whimlen, February 17, 2021 (Accessed March 22, 2022).