Keiko Nagumo is a 38-year-old teacher at Seikyo School. She possesses grey hair, olive eyes, and stands 1.59 meters tall with physical measurements of 93-61-88. She is also the mother of Sae, a student at the same school, placing her in dual roles of authority at home and in the classroom.

The narrative focuses on her relationship with Jun, a student. Despite her daughter Sae's interest in him, Keiko becomes romantically involved with Jun. This inappropriate relationship creates a complex dynamic. Her interactions with Jun extend beyond academics, crossing professional boundaries. The story centers on the consequences of this forbidden relationship.