Kippei Katakura is a high school playboy who fills his days with any girl he can. In reality, he only has eyes for one girl in particular—Kokoro Tokunaga. One day, Kippei's family introduces him to his five-year-old cousin, Yuzuru Sakashita, whose mother has abandoned her. Kippei is assigned the task of being Yuzuru's caregiver until her mother returns, and the young girl quickly grows attached to him.

Through Yuzuru's influence and the intimate bond that forms between them, Kippei learns not only about childcare, but also about developing meaningful relationships. As Kippei balances his time between Kokoro and Yuzuru, they all grow together and learn more about each other, their feelings, and the true meaning of family.