Maruo Eiichiro is a serious and pragmatic high school boy. In order to solve the problem of insufficient exercise outside of classroom learning, he participated in the free trial event of the South Tennis Club (STC) by chance, and met a female student from the same school, Takasaki Natsu. After talking with Takasaki and considering his own interests, he decided to join STC and began his tennis career. Eiichiro took the words "As long as you can catch up with all the balls and control all the balls, theoretically you will not lose." as a belief and worked hard towards the goal of professional tennis.