This story is a fantasy. Read it or don't but don't judge.

So my name is Adam and I'm 15. My little siter Emily is 13. We're pretty close since it's just us and our mom and she works nights a lot.

Like most guys I know I'm really horny a lot. Anyway, lately I've been noticing how sexy Emily is getting. She's always been a lot of fun and pretty but lately I've noticed that she's getting a really hot body too. She's only about 5 foot 2 but she's got really long legs for her height and she's into soccer and cross-country at school so she's in great shape. She's blonde with blue eyes and I know the guys in her grade all crush on her.

So the other night we were watching TV and mom was working. We were watching America's Got Talent and this really bad singer was on. I said there was no way he'd get through but Emily bet me that he would. He did so I asked what her reward was. She said I had to give her a backrub. No big deal since we are always doing stuff like that for each other so I said sure.

She grabbed a pillow and lay down on the carpet in front of the couch. She was wearing little yoga shorts under her t-shirt and I couldn't help checking out her ass as she got settled. I got off the couch and straddled her and started giving her the backrub I owed her. She was on her elbows so she could watch TV and had pulled her hair to one side so it was out of the way.

Well after a few minutes of rubbing a comercial came on and she lay down flat and put her arms at her sides. "Rub harder I'm really stiff from soccer" she asked as she lay her head on the pillow. I repositioned a bit so I could get more strength and really give her a good massage. When I was working her shoulders I realized my cock was pretty much right against her tight little ass. For a second I thought I was going to get a hardon so I moved down a bit to do her lower back for a while.

After a few minutes she said "Hold on. I have a better idea." She got up (giving me another great look at her round ass in her yoga shorts and those long legs) and went to the other room. She came back a moment later with a bottle of lotion.

She lay down again but this time pulled the back of her t-shirt up so I could put the lotion on her back. I was frozen there looking at the perfect skin on her back and at her tight ass that was no longer half hidden by her t-shirt. When she said "help me" it sort of broke the trance I was in and I moved over and helped her get the t-shirt up over her shoulders so her full back was exposed and the front of her shirt was barely still covering her tiny boobs as she lay back down.

I took some lotion on my hands and rubbed them together and then started to massage her again. "Ooooh yeah," she said, "that's soooo much better". I was really enjoying putting my hands all over the soft skin of her back and shoulders. There was no avoiding getting rock hard at this point so I was careful to prevent any contact. My cock was straining against my boxers and I pulled my own t-shirt down to try to cover it a bit in case she turned around.

In this position it was hard to get to her shoulders so I moved down to do her lower back. This of course made it easier to keep my cock from pressing against her ass but it also meant I was staring right at that cute, round ass as I rubbed the lotion into her lower back. I was getting so turned on I could barely stand it. She had her head on the pillow so I felt sure she couldn't see me without moving a lot so I took full advantage and got a really close look at her perfect little bum, her thighs, the glistening skin on her back ... trying to take mental pictures.

After a little while she said "Can you come up and do my shoulders some more? This is really the best massage ever!" I was nervous but so horny I couldn't think straight anyway. I moved up to her shoulders and at first was able to sort of hover just barely over her ass so she couldn't feel my hardon. I looked down and could see how close my cock was to her perfect little ass in those tight yoga shorts. Not even half an inch plus the thin fabric of her yoga shorts and of my boxers.

"Mmmmm. Harder please? If you can? I know you've already been rubbing for a while but just a little more okay?"

I moved a little further up and as I pushed down on her shoulders with more strength I felt my cock brush against her ass for the first time. At that exact moment she let out the biggest moan yet "Oooooh wow that feels amazing Adam!". I was pretty sure she meant the massage but part of me wished she had meant my cock against her ass. I kept working her shoulders harder and each time my cock would brush against her ass. Sometimes just barely, sometimes it would be pressed against her for a second or two hard enough that she HAD to notice. But she didn't let on and I was way too horny to stop doing it.

After a minute or two it seemed like she was moving in rythm to my massage. Each time I would press against her, my hands on her upper back and shoulders, my cock pressing against her ass, she would rock a little bit and it seemed like she was pushing her ass back into me.

My cock was throbbing and I could feel that if I didn't stop soon I'd come right in my shorts! I was so horny that I didn't even stop to think about what might happen if I did. My eyes were racing all over her sweet little body. The soft, silky skin of her back, her long, slender legs, her sides and the tiny hint of her stomach and small boobs I could imagine so clearly. And her tiny, tight, round little ass in those skimpy yoga shorts.

I wasn't even trying to keep her from noticing now. With each stroke of my hands up her back I was thrusting my cock against her upper thighs and ass. She was moaning with each one and I closed my eyes and imagined that I was fucking her. I pictured us in the same position but instead those little yoga shorts were down around her knees and my boxers were long gone. I imagined my cock disappearing between her thighs and pushing against her hot, wet little pussy. I imagined what it might feel like to have my cock inside that warm, tight pussy.

I grinded my hips into her ass one last time and felt an explosion as I came in my shorts.

Immediately I was aware of how stupid it was. There was no way she wouldn't realize what I had done. I still tried to play it cool and rolled off her right away. I jumped up and quickly headed out of the room saying "Okay that's all you get - my hands are tired and really greasy." I made it out of the room before she'd even have a chance to look up and hoped that she wouldn't figure out what had happened. I mean, do 13 year old girls even really know about that?

I washed up in the bathroom and stuffed my soaked boxers to the bottom of the hamper and put on clean ones. I tried to act cool when I came back into the living room. Emily was curled up on the corner of the couch looking relaxed but normal. I half expected she'd be staring at me or calling the cops or something. LOL. I grabbed a pop from the fridge and brought her one too. She took and said "Thanks" with a little smile and I relaxed a bit. At the next commercial she said "Adam that was the best massage ever! You give such great backrubs!" I looked at her to see if she was teasing me or about to say something else (like "...and you're a pervert!") but she didn't. I relaxed a little bit after that.

I can't wait to see what happens next time I lose a bet to Emily! Actually, I hope I win the next bet because I have some ideas on what I'd want for winning.