My girlfriend's older sister, who always wears sleeveless bras that expose her breasts without realizing how seductive she is, noticed my erection. So, I secretly performed a plank position with her and gave her oral sex, repeatedly bringing her to orgasm. (Shishido Riho, DOCZ-003)

Her sister always wore a sleeveless bra, her breasts completely exposed. Looking at her exposed breasts, I couldn't help but stare, even knowing I shouldn't. She always caught me looking, and this time was no exception. While resting in the living room, I ran into her sister. Her sister's breasts were still completely exposed. I looked at her breasts, and her sister looked at me too. "What are you looking at?" I was nervous. I could only say I was just looking at her. Her sister said, "You're getting an erection, aren't you?" I was so embarrassed. Her sister had seen through me. I didn't want to tell my girlfriend this secret. From that day on, I began hiding behind my girlfriend, secretly being seduced by her sister. Whether I was sleeping or in the bathroom, whenever she wanted, I would be seduced by her. Her tongue would entwine around me, making me lose all thought. Her beautiful buttocks would bounce in the air, shattering my reason. Her sister even wouldn't let me ejaculate without a condom… Ah! Forget it! That's it!