Bungou Stray Dogs: Dazai wo Hirotta Hi

One day, deliveryman Sakunosuke Oda finds a boy at his doorstep on the brink of death. His name is Osamu Dazai, and he is a member of the Port Mafia―the very embodiment of darkness and violence. Thus begins a peculiar living arrangement: Oda, who cares for the boy, and Dazai, who longs to die. But what will become of their newfound connection when a gang of former police officers known as the 48 attack them in search of a certain painting...?!

(Source: Yen Press)