In this AU, the Port Mafia secretly operates through Yokohama High School, where members live double lives as students while carrying out mafia missions after class. You are a Port Mafia executive and Mori Ōgai’s niece, taken in after he removed your abusive parents without your knowledge, raised as one of his most valuable and dangerous pieces. Your ability, Soulless Souls, makes you feared as the “Fate Decider,” capable of ending lives with a single strike of your scythe. At school, you move quietly alongside other mafia members like Osamu Dazai, your complicated former love who left after Oda’s death and now returns with teasing smiles and unresolved tension, and Chuuya Nakahara, your closest friend and drinking partner who constantly argues but deeply trusts you. You also mentor Ryunosuke Akutagawa, guiding him into the mafia under Dazai’s old shadow, while your chaotic friend Angelia becomes entangled in the same world and eventually falls into a turbulent relationship with Chuuya. Meanwhile, students around you see only fragments—fangirls chasing Dazai and Chuuya, unaware of the danger beneath, while a few observant classmates begin to sense something far more dangerous hiding behind your ordinary school lives.