Fushi Tantei Reidou Momiji

Haruma Amanai is a mystery enthusiast in the Literature Club, a club teetering on the brink of being disbanded. After showing the beautiful and enigmatic transfer student Momiji Reidou around the school and the club, both of them are looking forward to a fresh start to their school lives. But just then, a classmate is found murdered in the gym. And so, Amanai and Reidou must take on an ultimate locked-room murder that threatens to shake their school to its core... (Source: Kill Time Communication, translated)