Ko Tanaka, a third-year student at Kawanuma East High and former student council president, balances part-time work and academics while sporting his signature glasses. Having attended middle school with Ichiro Sato and Rin Suzuki, he sustained a lasting friendship with both. Initially grappling with moral reservations about pursuing a teacher, he resolved to secure a girlfriend before graduation.

Frequent encounters with school nurse Chizuru Tachibana entangled him in compromising scenarios. After confessing his feelings and facing rejection, he later earned her reciprocation post-graduation, sparking a mutual confession that ignited their romance. A bonus chapter depicted their first intimate encounter at a love hotel.

Subsequent arcs saw their relationship blossom into marriage, followed by the arrival of their daughter, cementing their family bond. The narrative further traces their enduring ties to peers through group appearances in final episodes and OVAs, underscoring their ongoing presence within the broader social circle.