#'actually dazai not being mentally ill would NOT make him better. to prove that here's his terrible normal cousin who is so normal'

[iwritenarrativesandstuff]

Dazai has a distant, well adjusted cousin named Shuuji who is ACTUALLY the evil mastermind of BSD. Thoughts?

My god. I think you've done it. I think you've solved BSD.

I hope it gets revealed scooby-doo style but everyone is just confused at the reveal because Shuuji looks identical to Dazai, kickstarting another several year long arc that is just a dramatic case of miscommunication.

Alternatively, Shuuji poses as Dazai for a bit then dramatically whips off the mask of his Dazai disguise, only for the Agency to just straight up not believe him and go back to their work because they think it's just more Dazai shenanigans that they are unfortunately used to. They keep dismissing the possibility as ridiculous, which makes Shuuji start to doubt his own identity. Ranpo, of course knows, but he is too busy grabbing popcorn and waiting for the guy to snap.

...or, most likely, he never even gets the chance to go in disguise because he's so painfully normal he's found out instantly.

Shuuji, pointing at Dazai: "Shoot him, he's the mastermind!"

Kunikida, aiming his gun at Shuuji with no hesitation: "The real Dazai would NEVER pass up a chance to die!"