I was in my sister's room, just killing some time, when she walked in on me jerking off. I was kind of caught off guard, but I tried to play it cool. She seemed a little taken aback at first, but then she started to get into it. It was kind of weird, but also kind of hot. She started to touch me, and I got even more turned on. I couldn't resist touching her back, and before long we were both naked and going at it. It was kind of like role play, me pretending to be her boyfriend or something. It was kind of awkward, but also kind of fun. We ended up having sex a few more times after that, and it was always kind of wild and crazy.