My parents remarried and on our first family trip, I shared a room with my sister-in-law! My sister-in-law has a bad sleeping posture, and while she was sleeping, her yukata came undone, exposing her breasts and panties! She then turned over in her sleep, right in front of me! Of course, I couldn't resist and started touching her timidly, but when I got carried away and started rubbing her vigorously, it seemed like my sister-in-law was awake too, and I thought she would get angry, but she got horny! What was supposed to be just a light touch turned into her wanting my dick! And then, in the course of things, we ended up crossing the final line...