Junya, who lost his mother a few years ago, lives with his father in the three-legged race. His father remarried Mayu, his partner, at the end of the summer when Junya was about to take the exam. For Junya, life with Mayu, who is too young to call her mother, is a series of confusions and temptations. It is inevitable that a boy who has just entered adolescence suddenly appears and realizes that his young mother-in-law is a woman.