Bungo Stray Dogs: Dazai Osamu No Nyusha Shiken (Light Novel)

Doppo Kunikida is a cutthroat idealist and member of the Armed Detective Agency, which specializes in dangerous assignments. In order to investigate a haunted house case, he teams up with the agency’s mysterious newcomer, Osamu Dazai. But the job quickly goes off the rails and ends up being more complicated than Doppo anticipated. And on top of that, it seems like the agency’s sworn enemies, Port Mafia, may be involved!
Notice: This book is written in Japanese.