Kippei Katakura is a 17-year-old playboy. When his 5-year-old cousin Yuzuyu comes to live with his family after her mother disappears, he is suddenly in charge of taking care of her. Kippei's main occupation changes from tending to his high-school girlfriends to picking Yuzuyu up from kindergarten and making her lunch. Soon the two are getting along like peas in a pod, but the girls at his high school miss their "quality time" with Kippei.