Manyû sanshimai: Ire kui rankô

魔乳三姉妹　入れ喰い乱交 (original title)

Synopsis

Irina, the third daughter of the three Nemoto sisters, is a plain, college science student who wears a white coat and glasses at school. It seems that things are going well with her boyfriend Soga. One day, while Irina is studying ancient Japanese history, she discovers a system in which women share a man sexually.