 I blame BSDW again. The preschool episode evoked an irresistible urge within me.

Chuuya finds his coworker...except they're not quite as he remembers. They've been turned into a child indefinitely by an unidentified individual's special ability.

Dazai is NOT a part of the Port Mafia. He in the Armed Detective Agency. All events take place three years after he vanishedfrom PM, after which he reappeared as a part of the ADA. The Port Mafia is enemies with the Armed Detective Agency (usually).