My name is Alex, I'm 15 years old, 5'5 and 150 lbs. Late one Saturday night, I was sitting at my computer playing the closed beta for Path of Exile. I was about an hour into it when my 9 year old sister came in and stood next to me. She's a little below 4 feet tall, weighing about 70 pounds, has long brown hair and hazel eyes.

"Hey Mary, what you doing up?" I asked.

"I had to pee," she said.

"Oh okay," I said and went back playing.

"Is it like Torchlight?" She asked.

"Yeah, but also very different," I said.

About a half an hour went by when I finally died.

"Can I try it, Alex?" She asked.

"Sure," I said.

I scooted my chair back and since it sits low, she had to sit on my lap to play. I moved us closer to the desk, she grabbed the mouse and started playing. She was not a beginner to these types of games as she plays Torchlight 2 on her own computer.

"Alex, pull the back of my shirt up, please...it's choking me," she said.

She lifted her ass and as I removed her shirt from under her, I got a glimpse of her bare ass. I just brushed it off, it wasn't the first time seeing it. She's a gorgeous girl, I just never looked at her sexually.

I was messing around on facebook while on my cellphone, when I received a text message from one of my friends. I clicked on the link and it took me to a video of a girl rubbing a cock between her ass cheeks. The girl had a gorgeous tight ass and at the end of the video, the guy shot his cum all over her lower back and ass crack. It was very hot and very much arousing.

The tent in my boxers grew till it pressed against Mary's ass. She didn't question what was poking her. She just continued playing the game while my cock grew harder and harder. My sister's excitement from the game eventually caused my cock to dislodged from her ass.

I was so turned on by the thought of my sister's ass getting me off that my mind was racing on how to get her to do it. I couldn't come up with a plan, especially one that she didn't have her freaking out. I decided to just jerk myself off. She was so occupied with the game, she would never know. My cock sprung free as I released it from my boxers. But before I took a hold of my six inch cock, I carefully folded the back of her shirt up to use her ass as a visual aid. I then took my cock in my hand and started stroking it. I was really getting into it, till Mary spoke.

"Alex, get closer to the desk," she said.

"Um...okay," I said.

As I pushed the chair forward, she slid back sandwiching my cock between her ass and my stomach. Her ass crack was positioned perfectly, only the head was poking out between her cheeks. Suddenly, the game excited her and as she moved, her ass rubbed against my cock. It felt amazing. Sadly though, it didn't happen often enough, but then an idea came to me. So, I started to slide my fingertips up and down her bare thighs.

"Alex, that tickles," she giggled.

I stopped and said, "Sorry."

"It's okay...it feels nice," she said.

I went back guiding my fingertips slowly up and down her thighs. After a few times, I went up to her hips, then around to her lower back. She squirmed and arched her back. I repeated the same route a few times, before I became bolder. I then laid my hands fully on her and started massaging her. I worked my way over her thighs to her hips then to her lower back.

"Mm," she moaned.

"Stop or continue?" I asked.

"Please continue," she said.

Each time I massaged my way to her back, I eased further and further up her shirt. My hands gradually made it up to her shoulders. Her skin was so smooth and warm. She moaned a bit as I massaged her back. After a minute or so, I dared to see how much further I could go. I slowly worked up and down her back, while easing my way to her ribs. She didn't stop me, so I continued around to her tummy. She had a nice flat tummy and as I rubbed my hands over it, she took a deep breath in and out.

I retraced my steps, from her thighs to her hips, up her back to her neck, over her shoulder blades, then back down along her ribs and over her tummy. I did this over and over again, but each time I came to her tummy I went higher. I was surprised when my hands went high enough up her front to where she had to move her elbows away from her body. When she gave me access to her breast, she and I took a deep breath in as my hands slid over her nipples for the first time. Her AAA breast felt awesome in my hands, especially her hard nipples. I slid them between my fingers as I caressed her little tits.

"MMmm," she moaned.

I slowly slid my hands down her front, passing her navel and going directly to her pubic area. I was tempted to go straight for her pussy, but I didn't want press my luck just yet. I ran my fingers through her little peach fuzz, then along the top of her thighs. I turned my hands inward and slowly massaged my way up her inner thighs till I was merely inches away from her pussy. She suddenly spread her legs apart. I was caught off guard by her invitation. I couldn't quite believe it. I slid my hands back up to her tits and caressed them for several seconds more. I then went back down to her tummy. I slid my hands to where her legs and hips meet, then slowly slid down both creases of her groin.

As I made my way down, she spread her legs apart and pushed her hips forward. My middle finger on each hand slid down the center of each crease, my ring and pinky slid down each inner thigh and my index fingers slid along the fuzzy outer folds of her pussy. The heat from her was amazing. I then lightly squeezed her pussy together and massaged up and down.

She let out a soft moan as I massaged her pussy with my fingers. I looked up at the monitor and noticed she stopped playing. Suddenly, she released the mouse and held onto the desk. She then started panting and grinding her ass on my cock. I then began squeezing her pussy together harder while pushing it away from her body. I would lighten up, then repeat over and over again. She became more vocal and started grinding on me harder.

"Oh Alex...mmm...t-that...mmm feels...sooo nice...mmm!" She moaned.

The tone of her voice was so hot and the feel of her ass rubbing against my cock was amazing. I was getting real close of blowing my load.

"Alex...?!"

"Yes?"

"I gotta pee!" She said.

"It's okay, Mary." I said.

"Oooh Alex!" She moaned loud.

She leaned forward and pushed her ass back hard against my cock. She started shaking and I could feel her pussy pulsating between my fingers. I couldn't take anymore. I grabbed her hips and repeatedly thrust up. My cock rubbed violently up and down her ass crack. My orgasm came hard. My cum shot up all over my shirt and on her lower back. She then laid back on my chest and I put my arms around her. My cock continued to leak cum while we sat there, both out of breath. After a minute or so, I could feel my cock shrink down the crack of her ass. Then the realization set in and I became worried. Is she going to freak out? Will I be in trouble?