My younger sister Rina is quiet and shy, and I thought she was a beginner when it came to sex. But when she got home, she started masturbating loudly! Then she brought in a much older man and seduced him by saying, "I want your dick!" The lewd sounds of a high school girl and an older man and the smell of a female stimulated my groin. And then I peeked at my younger sister indulging in a messy sex session with a middle-aged man. I never thought I'd be found out...