I heard a strange voice coming from my sister's room. Is it a moan? Or is she masturbating? Wow, seriously? I'm going to embarrass my sister who always makes fun of me... I rushed into her room thinking that, but she tried to cover it up, and I was found guilty. After that, every time I heard her moaning, I went into her room and persistently stopped her from masturbating! (I'll get conclusive evidence with my smartphone Itsuka.) At that point, I didn't realize that my sister's sexual frustration had reached its peak. And later, while I was secretly taking pictures of my sister masturbating, that tragedy (it still makes me horny when I think about it) happened.