AU in which the female versions of Sam and Dean exist and they used to be hunters. A new, "last" case brings them to Missouri, where the Winchesters are working on it already. They meet.
(It can be read as a self insert fic because it's going to be narrated from the original female character's perspetive, but she's named already to fit the narrative.)
A case comes up at a councelling retreat and Sam, Dean and Cas go to check it out. Sam snatches up the only job vacancy forcing Cas and Dean to go in as a couple.
None of them expect the events that unfold (but they kinda do).