At the Engetsuza Shrine, a mystical legend unfolds through generations, revealing the consequences of a male heir's romantic entanglements. Kounosuke, the unassuming son of the shrine's priest, leads a typical high school life, devoted to his childhood friend, the easygoing Shu. However, when an unexpected realization dawns upon Kounosuke one fateful morning—that his feelings have shifted towards Shu—a peculiar transformation begins to take hold of him.