An alternative universe is a setting for a work of fan fiction that departs from the canon of the fictional universe that the fanwork is based on. For example, an AU fanfic might imagine what would have taken place if the plot events of the source material had unfolded differently, or it might transpose the characters from the original work into a different setting to explore their lives and relationships in a different narrative context. Unlike typical fan fiction, which generally remains within the boundaries of the canon set out by the source material, alternative universe fanfic writers explore the possibilities of pivotal changes made to characters' history, motivations, or environment, often combining material from multiple sources for inspiration. AU stories are also sometimes used in official, though typically non-canonical, storylines, written by the creators of the original canon material.
Types of AU fan fiction
Authors and readers of AU fanfiction enjoy it for many different reasons, but there are several shared story types that exist within many fandoms: alternative timelines, contextual reassignment, "reality" swaps, crossovers, and predictive fiction.
Alternative timelines
Stories with alternative timelines follow the established canon before veering away at a crucial moment, similar in concept to many entries in Marvel Comics'What If series and DC Comics' Elseworlds series. Some alternative timeline stories are called "fix-it fics" because they rewrite the story so that the consequences of events are undone, although beginning events are the same. Others are called "denial-fics" because they ignore certain pivotal events in a given canon. Another example of a subgenre of the alternative timeline story is called a "do-over fic", similar to "fix-it fics" in which consequences of an event are undone, but in do-over fics particularly the entire story is reset to the beginning, and the author creates an alternate timeline that diverges from the original canon of the work.
Plot switch
Plot switch stories take the characters from a series and place them in another time, place, or situation. A subset of this type called "familiar plot switch" takes the characters from a series and places them in a setting more familiar to the author. This type of context shift is one of the main sources of "high school fic" in which all the characters are written going tohigh school.
"Reality" swaps
In a reality swap alternative universe —often in movies or television shows—the actors may find themselves in the fictional universe, the fictional characters may find themselves in the "real" universe, or the story may feature swaps both ways. This type of AU has appeared in mainstream publications as well. In Star Trekshort stories written in the early 1970s, the actors from the Desilu set were swapped with the "real life" Starfleet officers via the transporter. These fan fiction stories were later published in official Star Trek books. This concept was also used in an episode of Supernatural, "The French Mistake". In the episode, the main characters Sam and Dean are transported to an alternative universe where they are actors named Jared Padalecki and Jensen Ackles, respectively, on a television show called Supernatural.
Crossovers
This type of alternative universe places two fictional universes in a situation where they interact, similar to reality swaps. Such stories sometimes involve "comparisons or conflict" between the combat prowess of the two universes, often involving the various strengths and weaknesses of the technology/magic of each world. This genre of fanfiction is distinct from plot switch in the fact that it usually involves characters from at least two separate series interacting with one another. Sometimes these stories involve the substitution of characters from one universe for those of another.
Predictive fiction
Alternative universes can arise inadvertently in fanfiction when the source material is released in a serial form so that fan works are written before further canonical information arrives. For instance, much Harry Potter fan fiction written in the nearly three years between the publication of Harry Potter and the Goblet of Fire and Harry Potter and the Order of the Phoenix was written as "continuation" fan fiction, but became AU as soon as the new canonical material appeared.
Changing canon
In alternative universe stories, characters' known motivations may vary considerably from their decisions in the canonical universe. The author of an alternative universe story thus can use the same characters, but send them down different paths to achieve a completely different plot. On occasions, a fanfiction writer creates a character which does not exist in the actual story that inspired it.
