Bungo Stray Dogs: Osamu Dazai and the Dark Era

Bungo Stray Dogs: Osamu Dazai and the Dark Era is the 2nd light novel of the series, mainly focusing on Osamu Dazai's past in Port Mafia and telling the reason behind him leaving the organization. Like the 1st light novel, Dark Era was adapted into the anime, filling in Episode 13 to Episode 16 of the series.

It consists of six chapters in total.

Summary
Before joining the Armed Detective Agency, Osamu Dazai was the youngest executive with the Port Mafia, the most notorious underground crime syndicate in all of Yokohama. When one of their colleagues suddenly goes missing, Dazai and fellow Port Mafia member Sakunosuke Oda are tasked with conducting an investigation...and at last, the reason why Dazai parted ways with the Port Mafia is revealed!

Chapters

 * Prologue
 * Chapter 1
 * Chapter 2
 * Chapter 3
 * Chapter 4
 * Epilogue

Involved Parties

 * Port Mafia
 * Mimic
 * Special Ability Department

Trivia

 * The story became an collaboration event of Bungo Stray Dogs with Love Heaven (its developer is the same as the one who created Bungo Mayoi)
 * It also became a collaboration event of Eighteen : Dream World.