My stepsister and her mother moved in with us when she was 3 and I was 13. She was a spoiled brat that I couldn't stand being around. But when she hit puberty and started to become a woman my view of her started to change. But because of our age difference, her being my stepsister and me being married me only admired her from afar.
After I graduated high school and got married my dad and stepmom joined a nudist resort. After a year or so they invited my wife and I to go with them. Personally I think it was so my dad and bi stepmom could see my wife naked but that's another story for another time. Because of the resort my sister had no problem being naked around me. Fast forward to her senior year.
We live in a small town and 4 houses away on the same street. Every few months our parents, who are swingers, would go to the resort or camping with friends and my sister would stay with my wife and I. As luck would have it my wife took our kids to visit her family while I stayed home because of work the same week our parents went out of town.
The first couple days of us being alone together we mainly just flirted with each other witch we had been doing for a while prior to this week. I also sleep nude so in the mornings I would get up and go to the kitchen to make coffee before getting dressed. At night I'd undress before walking down the hall to take a shower. She wouldn't walk through the house naked but there were times she'd have on just her underwear. Just like at the resort we would pretend not to notice the other but I would always catch her checking to see if I was or not and try to hide a grin when she'd see me watching her. When she would take a shower I would go into the bathroom and talk to her. I loved watching her through the semitransparent shower curtain. She is 5'4" reddish brown hair with the light skin and freckles to go with it. She also played sports all year round so she had an athletic hard-body with perfectly round butt-cheeks that just beg to be touched.
Even with all the flirting and some light touching we had done for a while now I was still nervous about going farther than she was willing and telling our parents or my wife. It was the third night when she was taking a shower and I asked her if she'd like a full-body massage when she was done. She said yes.
When she got out of the shower I went to my bedroom to get the bed ready. I got the massage oil out and laid a towel on the bed to keep from staining the blankets with the oil.
A few minutes later she came in wearing a matching black lace bra and thong. The sight of her wearing that knowing she had put that on just for me made my already firm cock get hard and stand at attention. She got a naughty grin on her face when she saw the rise she got out of me.
She laid face down on the bed. The thin piece of lace that disappeared at the top of her ass and reappeared at her pussy which was also trying to swallow the thin fabric made my cock throb as I got on the bed and straddled her.
I ran my hands from her hips up to her bra where I unhooked it. As she was removing her bra I grabbed the oil and rubbed it into my hands. When she settled back down I started massaging the oil onto her. Rubbing from the top of her thong to her neck. Making sure to press my throbbing cock against her firm round ass every time. As I massaged her she started to ever so slightly lift her ass to meet my cock.
After several minutes of massaging her back I moved down so our knees were next to each other and oiled her ass and legs. Putting my knees between her legs so I could get oil on her inner thighs which of course gave me a perfect view of my ultimate goal. With her legs spread her puffy young pussy lids opened just enough to take in the thin lace fabric trying to cover them. While massaging her ass I made sure to do it in such a way to spread her cheeks an expose her asshole being cut in half by the string of her thong. Massaging her legs I would start at her knees and go up to her soft shaved pussy making sure to do it in a way that made her pussy open even more. After massaging both legs in this way it made so lace fabric that was supposed to be covering her pussy now was being devoured by her beautiful mound.