Crossover & Fusion Tags on AO3
When two fandoms collide — crossovers, fusions, and shared-universe mashups.
Crossover and fusion tags mark the fics that refuse to stay in one fandom. A Crossover brings characters from different canons into the same story; a Fusion drops one fandom's characters into another's world. Both are playgrounds for fans of more than one thing.
These tags help you find the specific kind of mashup you want — a true meeting of two casts, or your favorite characters reimagined inside another universe's rules. This guide explains the distinction and the tags that signal each.
The 4 tags in this group
Crossover
Brings two or more separate canons into contact: the detective meets the time traveler, the starship picks up a wizard, two unrelated casts discover they share a city.
Crossover Pairings
Flags romance across fandom lines: a ship whose two halves come from different canons entirely.
Crossovers & Fandom Fusions
The canonical umbrella that AO3's wranglers use to gather both traditions — worlds meeting and worlds merging — under one filterable roof.
Fusion
Merges canons instead of introducing them: one fandom's characters are poured into another fandom's world, replacing or becoming its inhabitants — the cast attends Hogwarts as students, pilots the Jaegers themselves, lives in the daemon-having universe natively.
Frequently Asked Questions
What's the difference between a crossover and a fusion?
In a crossover, characters from two or more fandoms meet within one story, each keeping their own world. In a fusion, one fandom's characters are placed into another fandom's setting or rules, without the second cast necessarily appearing.
Do I need to know both fandoms to read a crossover?
Often, but not always — many crossover authors write so the story is followable from one side. Check the tags and summary; some are built as an accessible entry point to the second fandom.
Read crossover & fusion tags fanfiction on the go
Fanfict Reader is the best way to browse, search, and read AO3 fanfiction on your iPhone. Download for free and start reading your favorite stories today.