Kiryuu Naoya becomes the private tutor of his friend Ohtakemaru's younger sister, who can't leave the house b/c of her fragile health. Strange occurrences keep happening around the Ohtakemaru siblings, however, and a rumor of a killer on the loose around the premises of their house have begun to circulate. Naoya also seems to have a secret that he doesn't want the siblings to know about, but all of this comes to light one night when...??