Reijou no Himitsu

Maejima Yukio the protagonist is a sophomore student at a private academy. He has a girlfriend Kashiba Miyu, she is introverted and does not talk much about herself or her family. However she and Yukio have been going out for a while and their relationship has deepened, that is when Miyu decides to invite Yukio to her house. There Yukio meets Miyu's sister Kaori and her strict mother Kimie...he soon develops a relationship with them too...