1(BSD)

An Au where abilities have a mind of their own and they choose their own users.

The abilities have a plane where they all reside until they find a human who they know will be the perfect person to be their user but sometimes they go for people they realize need a way to protect themselves and those they loved.

Of course that they never accounted how greedy or evil humans could be as some used their users or forced them to choose who they wanted as users but luckily more often then not things got resolved well.

But there is an ability that always refused to choose a permanent user and habited other abilities' users for a short time when they felt like it.

Said ability is the famous Book everyone is obsessed with finding and using so the other abilities and even the Book seeing this, choose the person who had no plans about using the Book or would easily give it up if they found about it to be the temporary user as the Book would be better protected like that as some humans found a way to enter their plane.

The Book choose to reside inside Akutagawa Ryuunosuke whose only wish was to be recognized by someone which would not affect the Book or lead him to use it(he is still the user of Rashomon, who is a protective little siblings to the Book who is the oldest ability to exist).

The page used by DOA? It was taken from a previous user of the Book and thankfully couldn't be used to track the Book.

Can the Book be stopped by No Longer Human? No, the Book is an ancient ability and such a young ability like No Longer Human can not affect it unlike the other abilities and the only reason No Longer Human works on Chuuya's ability is because the ability knew Chuuya could die if he used it's full power so they made it possible for No Longer Human to be able to stop it when Chuuya's ability is much older then No Longer Human.

Will anyone ever find out that the Book resides inside someone? Maybe but how they would find is the better question.

Anyways, anything else is up to the writer and if the writer wishes they can change who is the current user of the Book