The spinoff follows Ryuunosuke Akutagawa, who vows revenge on a man dressed in black in order to rescue his sister. However, as he is about to starve to death, a man from the Armed Detective Agency appears.

The story begins with an attack on humanity by giant indestructible monsters named "Enemies". The Enemies drive humanity to the brink of extinction... but the one to save the world from the depths of hell is a lone boy!
The SF novel series by Kafka Asagiri (Bungou Stray Dogs) jumps into the manga scene with art by Anri Sakano (Sayonara Peter Pan)!
Is he God or is he the Devil...will the amnesiac protagonist Kyle Kamishiro bring a future filled with hope, or...!?

Nakajima Atsushi was kicked out of his orphanage, and now he has no place to go and no food. While he is standing by a river, on the brink of starvation, he rescues a man whimsically attempting suicide. That man is Dazai Osamu, and he and his partner Kunikida are members of a very special detective agency. They have supernatural powers, and deal with cases that are too dangerous for the police or the military. They're tracking down a tiger that has appeared in the area recently, around the time Atsushi came to the area. The tiger seems to have a connection to Atsushi, and by the time the case is solved, it is clear that Atsushi's future will involve much more of Dazai and the rest of the detectives.