Kō Tanaka is a 17-year-old male third-year student at Kawanuma East High School and former student council president. Sharing a junior high background with Ichirō Satō and Rin Suzuki, he possesses long-standing friendships with them. Physically, he has brown hair cut to neck length and black eyes. Having secured early university admission through recommendation, Tanaka enjoys stable future prospects. Despite this advantage, he chafes at his lack of romantic experience, setting a goal to find a girlfriend before graduation. This ambition becomes complicated by his growing attraction to the school nurse, Chizuru Tachibana, whose cold demeanor and expressionless attitude toward students earned her the nickname "Absolute Zero" Tachibana. Throughout his final high school months, Tanaka frequently encounters Tachibana in compromising and embarrassing situations. These repeated interactions spark romantic feelings, leading him to confess his attraction. Though Tachibana initially rejects him, their relationship develops significantly after his graduation, culminating in her reciprocating his feelings and confessing in return. They become a couple. Their relationship progresses to marriage, a status later confirmed within story arcs involving other characters, such as the "Kurisu Kurumi & Nanjo Nana Arc". Their union results in the birth of a daughter, cementing their family life beyond the high school setting.