I have a precious sister. Ever since my mother died when I was young, she has always been a substitute for my mother. She has always been by my side, in place of my father, who is often away on business trips. She is always by my side, even in hard times - when I feel lonely, when I feel sad. Even when I feel happy. She is an irreplaceable and precious person. That's why I thought she would always be by my side. Until I heard those words from Mayu's mouth. "You see, big sister has a boyfriend now♪" From that day on, the relationship between me and Mayu changed. Mayu, who was a virgin, was given sexual pleasure by a man, and her innocent body was gradually developed. And all I could do was watch Mayu change. I decided to accept this reality, even though it was hard to do so, because I wanted her to be happy. But there was a strange rumor about that man. “It's just for fun, of course she's a bitch.” "But I feel sorry for Taku-chan, having such a slut as a family member." "To you, she's just a precious little girl, but to us, she's just a cum toilet." An ADV where you can only watch as your beloved sister is deceived and played with by a man who only cares for sex. [From Official Developer Website Translated Via Google Translate]