Your gateway to endless inspiration
I love how in BSD every au and fanfic that someone makes could be true.
Person A came up with a pirate au, cool let's write it into the Book and see if Odasaku lives in this one or if Dazai decides to stop being a pirate and go join some other sea faring crew instead. Magic and Mystery? Sure why not? The aus where Dazai and Chuuya got to UA? That too.
There is a book that can create countless alternate realities, which means that any of them and every of fic technically has the chance to be true in one of them.