After six years away, Hassaku Tamao returns to his rural hometown to work as a high school teacher. As a child, he had made a casual promise to four close friends—that they would one day get married. Tamao has long since forgotten the pledge, but the girls, now beautiful high school students, have not. Almost as soon as he arrives, all four confront him and insist he honor the childhood vow, throwing him into a chaotic love pentagon he never asked for. The story unfolds as a comedic romantic struggle, with the heroines each pursuing Tamao with their own distinct personalities and motivations. Flashbacks gradually reveal the history behind each girl's feelings, showing how Tamao, as a child, gave each of them a reason to fall for him. Meanwhile, Tamao, who tries to maintain a professional distance as their teacher, finds himself drawn into their escalating affection and must navigate his own growing awareness of their relationships. The narrative balances lighthearted, slapstick comedy with sincere romantic moments, and the romantic rivalry deepens as the heroines compete for his attention while also supporting each other's personal goals.