Based on the erotic game by Zero.

Shiori and Saori are twins, and they have a secret crush on the "oniichan" that lives next door. Recently they developed an interest in H. "I'll have "oniichan" teach me various things."

When summer comes he is asked to look after the house and the girls by their mother. Since its summer vacation there is a lot of free time. How fun can house sitting become?