Finn is in an arranged marriage with another character, they haven't know each other for long but they still like each other to be willing to make it work. Before their wedding day though, through some unexpected circumstance he ends up married to someone else and has to try and get back to their fiancé.

It can be a true Corpse Bride AU or just the accidental marriage part. I'd prefer if it was either an in universe AU or something supernatural than a modern AU, but that's more of a preference than something mandatory. An OT3 ending is fine too instead of the more tragic movie ending.

If you use Kylo or Rey for the other characters I just ask for no Reylo.