In Episode 1 of Classmate no Okaasan (also known as My Classmate's Mother), the story introduces Jun, a second-year high school student at Seikyo School. Jun harbors a secret crush on his teacher, Keiko, who is significantly older than him. Keiko, a widow and the mother of Jun's classmate Sae, teaches at the school and oversees the badminton club, which Jun joins. The club has no other members, allowing Jun to spend time alone with Keiko during practice sessions. One day, Sae approaches Jun and reveals that her mother often talks about him at home. This conversation leads Jun to discover that Keiko's husband passed away ten years ago, leaving her a single mother. This revelation becomes a turning point for Jun, as he decides to confess his feelings to Keiko, despite the societal taboo surrounding their relationship.
