Hell Is Dark with No Flowers, Vol. 4 (light novel)

A MYSTERY ABOARD A MOVING TRAIN!In response to a challenge from Ibara, Shiroshi and Seiji head to a luxury sleeper train to put an end to the competition over Hell once and for all. On board, they find six other passengers, and hidden among them, an executioner. As a series of murders begins, Shiroshi must take on the role of detective and stop the killing before the night is out!