It was at least 7 inches long and very thick, Katie's hand looked tiny around his huge shaft and my own cock started to harden and throb as I stared a... his beautiful cock. I wanted to keep watching but I knew it was wrong to look at my sister so very reluctantly I stepped away from the wall and lay down on my own bed, stroking my penis and thinking about what I had just seen. I could hear them through the wall, Katie was obviously being fucked hard and fast as I could hear her moaning and. Then even when she wasn't swimming, she started walking around the house in just panties and a T-shirt, most of the time she didn't even bother to wear a bra and trust me I could tell.When we watched TV at night now, she sat right next to me on the couch. She'd often lean over and touch me accidentally or brush her legs or breasts against me. As a scientist I could see that she was gathering information.Then it happened. My house is fairly isolated and we got a big thunderstorm one night. I was. She thought some more about it all. She thought about what happened with him. Could she make him feel that good like she did earlier? Back in her own room, alone, she kept on thinking about it all. Oh my fucking God, daddy that was soooo fucking good to me. Let me do what we did earlier again she told herself. You were incredible. Your cock was huge daddy! And how you felt in my hands as I…as I held it in my mouth, she told herself excitedly. What else can I say? Ohhhhhh wow, yes…when you and I. “Please indulge me.”Indulge her? Hell, I wanted to fuck the crap out of her. In an instant, she was fumbling with my belt buckle and forcing her hand in past the waistband of my blue jeans, feeling for my rapidly expanding tool. I don’t think I could have stopped her, even if I wanted to. She was determined and very focused.There was no turning back at this point. I unzipped my jeans to relieve the pressure that had built up. She tugged at my jeans and then pulled them downward, as she fell to.