Makoto Kurobe has always found his stepsister, Mai, quite boring. Rather, nothing in life really interests him—save for the glee that comes from taking the lives of animals. However, over the years, he has longed to up the ante and try out a new type of victim. Therefore, it comes as no surprise when he kills Mai and uses her body to kick off a class-wide death game. Standing amidst the school's halls, dyed red under the moonlight, the mastermind behind it all is Makoto—that is how the story of a manga from Mai's previous life went.

When a reader of this story is reincarnated as Mai, she resolves to rescue her brother from his own plan. Aware of Makoto's psychopathic tendencies, Mai does whatever she can to spark in him an interest in life, but a person's nature is not so easily changed. As Mai carries out her plan, Makoto's twisted mind—which has always been obsessed with death—turns its attention to a new target.