Zasshono Academy is a very large private school with a total of 54,000 students from elementary level, to junior high and high school. Among the large number of club activities at the school, one club is quite unique:The Eiken Club. The activities of this club are shrouded in mystery, and strangely enough all the members are excessively busty, headstrong female students, like Shinonome Chiharu, the top scorer in the entrance exam.

The newly arrived high school boy, Mifune Densuke, is forced to join the Eiken Club, and in an instant, his dull life so far turns up-side down, with intense passion, romance and much trouble!