Eiken is a heavily fanservice-themed manga and anime series created by Seiji Matsuyama. The story depicts the life of schoolboy Densuke Mifune after he is forced into the mysterious Eiken Club, which is populated only by females, several of whom have ridiculously enormous breasts.
The manga series ran for eighteen volumes, and additionally included a series guidebook. A number of radio drama episodes and a two episode OVA have been produced.
The first twelve manga volumes have been released in North America. The first three volumes were rated 16+, while subsequent volumes were rated 18+.