Bungo Stray Dogs: The Untold Origins of the Detective Agency

Origin of the Detective Agency: Untold Story is the 3rd light novel of Bungo Stray Dogs. It tells the forming of the Agency 10 years before the main timeline, as well as the meeting of Yukichi Fukuzawa and Ranpo Edogawa.

The novel also tells a little bit of Sakunosuke Oda's past as an assassin.

Summary
Ten years before the events of the manga series, a fateful encounter brings a professional bodyguard named Yukichi Fukuzawa and an arrogant boy genius named Ranpo Edogawa together. The result: the establishment of the Armed Detective Agency, an organization that takes on dangerous jobs even the police won't handle!

Chapters

 * The Daily Routine of a Detective Agency
 * Origin of the Detective Agency: Untold Story

Post-Conflict

 * Sakunosuke Oda later quit his assassin job after meeting Natsume Souseki.
 * Sometime after the agency's establishment, Kunikida and Yosano joins in.