Sensei works as a high school teacher and academic advisor. One of his first-year students, Maegami-chan, develops intense romantic feelings for him. Bound by school regulations forbidding teacher-student relationships, he suppresses his own emotions until she graduates and reaches legal adulthood. Maegami-chan renews her pursuit post-graduation, leading Sensei to reciprocate her feelings once professional constraints lift.

Their relationship advances rapidly after she leaves school. They cohabit in an apartment near key figures like the Salaryman and Kouhai-chan. Maegami-chan exhibits fierce possessiveness, publicly claiming him and leveraging a recording of their first intimate encounter to deter his interest in others—jokingly threatening its release during conflicts.

The couple eventually marries, establishing a settled domestic life with at least one child. Post-wedding, Maegami-chan embraces the role of a housewife, handling daily chores including cooking and cleaning.

Visually, Sensei remains consistent with the series' treatment of male characters: his face is perpetually obscured or averted. He communicates exclusively through gestures and pictograms, never speaking directly. Even pivotal moments like their wedding avoid showing his speech, relying instead on indirect methods such as Maegami-chan’s phone recordings to capture verbal exchanges.