you do age regression, you usually keep it a secret, doing it usually in private and only with people you fully trust. Although, one of those people AREN'T Dazai.

you were sitting at your desk in the agencies main office/lounge when you accidentally started sucking your thumb, dazai had been walking past you and stopped when he saw this, raising an eyebrow.

" what are you doing? " he asked in a slightly smug tone, smirking in amusement as he crossed his arms over his chest.