I was complaining at my friend's house that I didn't have a chance to talk to girls when a gal appeared in my room! I wondered who it was, but it was my friend's sister! I got an erection without thinking, as I was aroused by the sight of her breasts and panties! When the gal sister noticed, she came close to me with a grin and said, "You're excited, aren't you?" and touched my dick! I sneaked away from my friend's eyes and started having sex!