Itsuki Kamiyama possesses a peculiar fascination with the grotesque and the macabre, showing a particular interest in disturbing murders. He can tolerate even the most hideous crimes committed by the most warped humans and is drawn to unsolved cases like a moth to a flame. However, he is not merely intrigued by these cases—he is also adept at solving them. While following the leads of an especially odd chain of crimes, Kamiyama becomes familiar with his classmate Yoru Morino. As he spends more time in her presence, he begins to realize that she is more like him than he expected. With every case he unravels, Kamiyama slowly starts to uncover Morino's carefully shrouded past. As Kamiyama's mask of normalcy steadily slips to reveal his dark tendencies, he finally allows himself to wonder—what if he were the one to take Morino's life?