My sister and I are very close. We spend a lot of time together - we hang out with the same friend group as well. She is around two years younger than me - although it's always seemed as though we were the same age - such was our bond. However, in our teen years, if there was one unspoken rule, it was that we don't mention sex or anything remotely related to it. If anything, strangely, that made us closer. One night though...
We were both enjoying a night in. Our parents were out of town and all our friends were either doing homework due for the next morning or other things. So Lucy and I decided the best thing to do was to get a decent film and watch it in the sitting room. Eventually it was she who picked the movie.
So as time went on, so did the most boring film in history. Nonetheless, I was with my lovely sister, so that was ok.
Then, all of a sudden the film started to get interesting, as it would have for any teenage boy at that moment. A sex scene appeared. Full on as well, a hot and completely naked girl kissing the nude man with a six-pack - all activity obscured by the bed-sheets. As would be expected, I began to get hard - but tried to hide it as my sister was only on the other side of the sofa. It was slightly awkward as we never spoke about anything sexual; but we cured the tension by looking at each other and giggling slightly. In retrospect, I think she knew then and there that I was horny.
Finally, I could take it no more. I simply had to masturbate. "Lucy," I said, "I think I'm going to lie down for a bit - I've got a bit of a headache. I'll be back in a bit".
She smiled and said "sure". With that I went upstairs to my room.
I threw off my shirt and pants and jumped into my bed. My cock was so hard and was throbbing in my hand - just waiting to be pumped. I started out by slowly moving my hand up and down - precum oozing out. I used this as my lube. It felt great, sliding my hand up and down.
I was doing this for about five minutes, when all of a sudden I saw a silhouette in the frame of my bedroom door. I then realised that in my haste I had forgotten to lock it. Leaning against the doorframe was Lucy, with a smirk on her face.
"I thought you ran upstairs a little too quickly for someone with a headache", she said, clearly trying to hold back a giggle, "though I didn't think you'd be doing this!" I realised that I was turning red from embarrassment. I had just been caught masturbating by my little sister!
"Okay, okay," I said, "it's just that that...scene from the movie made me a bit horny."
"I know, it was the same with me - I just hid it better than you did."
"So, you do this as well?"
"Yeah, everybody our age does it! In fact, can I do it with you? I need to rub one out after seeing that scene!"
With that, Lucy took off her dress, bra and panties and joined me on my bed. I had never known just how amazing a body she had. She is slim with medium sized tits - rather like a cheerleader. We were sat directly next to each other. She spread her legs and licked her fingers before starting to rub. I began jacking faster until I got into my rhythm. It wasn't long before Lucy started moaning from pleasure. She entered two fingers into herself as she got more and more into it. Her body moved up and down in response to the fingers being thrust in and out of herself - her hand playing with her right tit - massaging it and pinching her nipple. Soon I could tell that she was ready to cum. She began to finger herself faster and faster and her breathing got heavier and heaver.
"Oooohh I'm just about there! Oh yeah! Oooohhhhhhh!"
Her body shook and she stopped as she had a huge orgasm. Seeing that sent me over the edge - I got to the point of no return and came hard all over my belly. She loved what she saw.
"Well, that was fun," she said. "I've never seen a guy do that before in real life. Plenty of times in porn, but this is a first."
"We really ought to do that more often," I replied. "One of the best cums I've ever had."
"Me too - definitely will be doing that again!"
We got dressed, went back downstairs and watched the end of the movie, just looking at each other every now and again. We have masturbated together ever since.