Losing a Tiger may be a Blessing in Disguise is the first chapter of Bungo Stray Dogs.
Atsushi Nakajima rescues a man named Dazai Osamu, who tried to commit suicide by drowning in a river. Dazai and his partner, Kunikida treat Atsushi to some bowls of chazuke as an apology while learning that Atsushi was kicked out of his orphanage. The two men introduce themselves as detectives who are looking for a tiger when Atsushi tries to excuse himself. The detectives grow suspicious and Atsushi confesses that he is being chased by the tiger and Dazai persuades him to help them capture it.