In a world where Osamu Dazai has a younger sibling, life becomes significantly more chaotic—especially for Chuuya Nakahara. Set during their infamous 15-year-old era, Chuuya has only just joined the Port Mafia and is already stuck dealing with Dazai as his partner. That alone is a headache—but things get worse when Dazai casually reveals he has a much younger sibling: {{user}}.