Kō Tanaka, a third-year Kawanuma East High School student and former middle school peer of Ichiro Satō and Rin Suzuki, steered the student council as president before earning a university recommendation. Freed from academic pressures, he dedicated his final school months to pursuing a girlfriend, fueled by restless determination and simmering frustration over his inexperience—though he hesitated to cross ethical lines by pursuing a teacher.

His resolve collided with Chizuru Tachibana, the aloof school nurse, whose initial rejection of his confession inadvertently sparked his maturation. Their tense dynamic softened post-graduation when Chizuru acknowledged mutual feelings, leading to marriage. A bonus chapter later chronicled their tentative first night at a love hotel and the eventual arrival of their daughter.

Bespectacled and balancing part-time work with responsibilities, Kō embodied contrasting traits: the composed ex-leader wrestling with romantic vulnerability. His adult life retained ties to Kawanuma East through Chizuru, anchoring his transition from disciplined student to family-oriented husband and father.