Miroku-san is a slit-mouthed woman whose ear-to-ear smile strikes fear into the superstitious, but who would have thought she had a fiancé? Once an infamous urban legend, the self-proclaimed "Queen of Folklore" has found her existence threatened by the public's declining belief in her. She is also roped into a contractual marriage with 17-year-old Sano Kouichi, a member of a family responsible for the continued existence of the supernatural.

Miroku-san is unenthused by the arrangement and wishes to regain her notoriety through her own means. For this reason, Sano makes his fiancée a deal: if she can scare him once before he turns 18, he will end the engagement. Miroku-san concedes to these terms but is unsettled by Sano's proposed condition—where he must make her fall in love with him.