Suddenly, my mother remarried and I suddenly had to live with my stepfather and step-sister. My sister Mai was stunned when she saw me for the first time. "I never heard that I was going to have a younger brother, or that he was one year younger than me. I thought he was about elementary school age." She may have been anxious about living with such a big brother. I felt a little sorry. However, after a week, we got used to living together, and my sister started wandering around the house in her loungewear, which was almost like underwear, and her big butt was sticking out. "Don't stare at me. We're at home, so it's okay to dress however you like, right?" No, no, if you dress that erotically, I can't stand it! I got an erection from her defenseless and sloppy butt, so I hurried back to my room and masturbated. My sister doesn't care about my sexual situation, and she shows off her erotic butt every day. My sister was dozing on the sofa in the living room with her ass exposed... I couldn't resist touching her big ass... It was so soft... I could get addicted to it... I was so absorbed in rubbing it that my sister woke up. "Hey, what are you doing? Stop it... we're brother and sister, aren't we?" I know that... but my reason has already been blown away... I'm sorry, mom! But I can't back out anymore!! I buried my face in her soft ass, rubbed my crotch against her ass crack, and then inserted it from behind... It's crazy... I can't stand the feeling of her ass rippling... It feels so good I pistoned it hard! Without thinking about the consequences, I injected my thick semen deep into my sister's vagina... I did it... incest... the family collapsed... The next day, my sister was calm. She didn't tell our parents... Maybe she didn't like it? I got carried away and started chasing my sister's ass when my parents weren't looking...