On her first day of high school, Yui is helped by a man whom she assumes is a teacher. It is later revealed that he is actually a fellow student named Daisuke. Despite being ten years older than other students, Daisuke has returned to high school to relive the teenage experience he missed out on in the Showa era. Yui takes it upon herself to help him adjust to school life and enjoy their youth together. The book also includes a bonus one-shot called "Irotoridori no Sekai."