Marin Mita's troubled face is so cute and precious... Marin has a timid and shy personality. She is unaware, but her appearance and gestures appeal to men and make her popular. A tutor is assigned to her. It's Atsushi, her sister's boyfriend. He was troubled. Even though they've been dating for a while, Marin's older sister is strict and he hasn't been able to do anything with her. Compared to his strong older sister, Marin seems weak and ready to go. Atsushi, whose desires were about to explode, couldn't help but touch his younger sister. However, Marin... accepted it. Atsushi's lust, knowing that she is weak to pressure, escalates more and more...