Mamoru Suzusato, the protagonist, attends an all-boys school in a rural area. He'll be graduating soon and begins scoping out prospective colleges to continue his higher education. One such college is Yaseda University. It's summer break, and he uses this opportunity to visit and stay at a dormitory run by the Souma family who happen to live very close to Yaseda University. Mitsuko Souma, the dorm mother and mother of the Souma household, is a cousin of Mamoru's own mother, which is why he's particularly drawn to staying with them. Mitsuko and her three daughters all live together there, and little does Mamoru know just how sex-hungry those ladies truly are...

[From Fakku]