Fifteen Chapter 1

Phase.01 is the first chapter of the Bungo Stray Dogs: Dazai, Chūya, Age Fifteen manga.

Summary
Years after a mysterious explosion that created Suribachi City, a Port Mafia member is cornered in an airplane by Sheep King Chūya Nakahara after attacking their territory, for which the mafioso explains that their arsenal had been attacked by the calamitous god, Arahabaki. At the mention of the latter, Chūya releases the mafioso from his gravity-manipulated hold and instantly kills him, vowing to kill all of the Port Mafia.

In his clinic, newly-instated Mafia boss Ōgai Mori gripes about the declining performance of his jurisdiction to fifteen-year-old Osamu Dazai. The boy insists on wanting to die painlessly, but Mori asserts his need for Dazai to live as the sole witness of the previous Mafia boss's death one year ago. During that time, Mori kills the then Mafia boss and straightens the story to Dazai that the predecessor has died of an illness after appointing Mori as his successor.

Despite Mori's seemingly perfect strategy, Dazai corrects him that he has made a mistake of choosing him as his accomplice. Though he can ultimately dispose of Dazai without earning suspicion due to his suicidal tendencies, Mori admits having made a miscalculation of choosing the nightmarishly cold boy as his accomplice; however, Dazai holds no apparent interest in such case. Mori then hands him a Silver Oracle to investigate rumors of the predecessor's alleged reappearance in Suribachi City.

Dazai and Mafia veteran Ryūrō Hirotsu stake out Suribachi City, where they gather testimonies of having witnessed the predecessor's appearance. Before heading back to report back to Mori, Dazai is assaulted by Chūya who asks him to spill out intel he has gathered about Arahabaki. Initially disinterested, Dazai recalls about the Sheep and their gravity-manipulating leader, recognizing the fifteen-year-old as the Sheep King, Chūya Nakahara.