A fifteen year old tennis player, whose most prominent feature is his hair, often called "rooster hair" by his colleagues.

Maruo Eiichirou is a diligent student and somewhat of a perfectionist. He earned his nickname "Ei-chan" because he keeps getting straight A's on his exams. Although an honor student, he lacks in exercise, and as a result, ends up joining the Southern Tennis Club (often abbreviated as STC).

He starts off as a naive beginner who has trouble in trying to catch up and learn the basics.

He has romantic feelings for Takasaki Natsu or Natchan, as he calls her affectionately, his fellow club and schoolmate.