Crossovers & Fusions Tags on AO3

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. In a crossover both universes remain themselves — characters keep their own histories and rules, and the story's spark comes from worlds colliding rather than merging.

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Flags romance across fandom lines: a ship whose two halves come from different canons entirely. These pairings are usually born from 'they would be perfect together' lightning strikes or actor-shared casts, and the tag helps readers find them since relationship filters spanning two fandoms are otherwise hard to browse.

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The canonical umbrella that AO3's wranglers use to gather both traditions — worlds meeting and worlds merging — under one filterable roof. Browsing it surfaces the full spectrum, from cameo-sized crossovers to total fusions, which makes it the right entry point when you want multi-fandom work without committing to one mechanism.

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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. Unlike a crossover, the second canon's characters usually don't appear; only their world does.

What it means →