I thought my stepsister, who came from my parents' remarriage, was doing something in my room, so I secretly peeked and found her having an orgasm by inserting a kotatsu leg into her vagina! I was so shocked by the sight that I couldn't look away, but then she noticed me, making the atmosphere awkward… She scolded me for masturbating in her room, but since my crotch was fully erect, I had no persuasive power at all! Seeing this, whether she was aroused or embarrassed and retaliated, my stepsister grabbed my dick saying she would teach me proper sex…
