Our protagonist has enrolled in Penile University, majoring in Perversion in order to study and deepen his understanding of the art, and eventually carry out research on the subject.

In order to get up close and personal with perverts, he becomes a lodger of the famous Maezono family, who live in Vaginville.

The Maezono household consists of a mother and her four daughters, each one of them a hardcore pervert.

[From MangaGamer]