Manga by author Asagiri Kafuka

From MangaHelpers: 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! [tethysdust]

Spinoff of Bungou Stray Dogs.

Bungou Stray Dogs Gaiden: Ayatsuji Yukito VS. Kyougoku Natsuhiko tells the story of the "homicide detective" Ayatsuji Yukito and his assistant Mizuki Tsujimura as they try and solve a mysterious murder case at the request of the government. Their search eventually leads them to Yukito's old nemesis and public enemy Kyougoku Natsuhiko.

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 are 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 Atsushifuture will involve much more of Dazai and the rest of the detectives!