Fifteen Arc is the first background arc of Bungo Stray Dogs. It tells the story of how Dazai met Chūya, and eventually joins Port Mafia.


The ghost of the previous boss haunts the Port Mafia. At fifteen, Osamu Dazai, under the careful eye of Ōgai Mori, receives his first mission to investigate the matter. The investigation leads him to Chūya Nakahara, the infamous "King of the Sheep", a rival group of juveniles. With his own past unknown to him, and the lives of Sheep members on the line thanks to the Port Mafia, Chūya agrees to work alongside Dazai in order to unveil the truth behind the Port Mafia's former boss.




From the Dazai, Chūya, Fifteen Years Old novel
  • Prologue
  • Phase. 01
  • Phase. 02
  • Phase. 03
  • Phase. xx
  • Phase. 04
  • Phase. 05
  • Epilogue



Participants Result
Chūya Nakahara vs. an unknown Port Mafia member Chūya kills the man
Chūya Nakahara vs. Ryūrō Hirotsu Chūya gains the upper hand until the previous boss appears and causes an explosion
Chūya Nakahara vs. GSS soldiers Chūya kills all the soldiers
Chūya Nakahara vs. Arthur Rimbaud Chūya defeats the man and kills him
Osamu Dazai vs. the previous boss Dazai nullifies Randou's Ability, making the boss disappear
Chūya Nakahara vs. Shirase Shirase stabs Chūya in the stomach with a poisoned knife
Chūya Nakahara vs. Sheep members and GSS soldiers Chūya uses his Ability to create a hole in the ground and hide himself
Port Mafia soldiers vs. Sheep members and GSS soldiers Dazai orders the Port Mafia soldiers not to kill the Sheep members as they are mostly children


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