Eiken(2003)

Eiken: Eikenbu yori Ai wo Komete

Densuke just enrolled at the exclusive Zashono academy. He's eager to participate in extracurricular activities, but he never expected to join the mysterious Eiken Club. Strangely enough, every other member is a busty co-ed, and many of the clubs activities involve bikinis. But Densuke isn't interested in anyone but the shy and beautiful Chiharu.

(Source: Anime News Network)