Kō Kitamura, whose family owns a sporting goods store, has known the Tsukishima girls since he was born. The Tsukishima family runs a batting center and cafe, and they have four daughters. There's Ichiyo, the responsible eldest; Wakaba, Kō's cheerful best friend; Aoba, who doesn't get along with Kō; and Momiji, the energetic youngest daughter. During the summer of their fifth grade, Wakaba leaves for camp after making a promise with Kō to go to the summer festival when she gets back. But she dies in an accident while at camp, and Kō goes to the summer festival by himself in mourning. When Kō enters high school, he aspires to lead his baseball team to the Koshien National High Schol Championship as their ace pitcher and make Wakaba's last dream come true.