My Sister’s Hands

My sister and I share the same birthday. We’re not twins though. We just happened to be born on the same day, but one year apart. I guess Dad was a busy guy back then.
Shortly after I turned sixteen and Marilyn turned fifteen I began to notice that my little sister wasn’t so little anymore. At fifteen years old she had already developed a rather large bosom and a very nice, curvaceous body. She was around five feet eight or nine and I guessed her to be somewhere near one hundred twenty pounds. She kept her hair short and parted on the side. She didn’t wear a lot of makeup, but then again, she was only fifteen and mom and dad didn’t approve of that sort of thing. She had definitely grown into a nice looking young woman. For me, we’d gone from being just brother and sister to her becoming the fantasy of my late night jerk off sessions.
As much as I fantasized about her coming to my room for raw sex adventures I knew this was something that was limited to the realm of my oversexed imagination. Still, I enjoyed it even if only in my mind.
The first time “it” happened was purely by accident. Mom and Dad had gone out to a dinner party and Marilyn was over at her friends house, or so I thought. I was in my room, on my bed with my computer monitor facing me, watching a really good porn clip. I had taken all of my clothes off so as to really enjoy my time alone. I had poured some oil over my stone hard cock and was slowly rubbing it up and down. Obviously, I was lost in the porn action because I didn’t hear Marilyn come home.
The way my room is set up the mirror on my dresser gives a perfect reflection of my bedroom doorway.
So, here I was stroking my cock in complete abandonment when I noticed a movement behind me. Marilyn was standing there.
My initial reaction was to pull the bedspread over myself, but something stopped me. Maybe it was shock or embarrassment or maybe something else, but instead of panicking I continued to rub my prick while my sister simply stood there watching.
The excitement of Marilyn watching me jerk off was a turn on I had never thought about before. In all my fantasies I had never given a moments thought to her watching me.
Before I realized how far along I was I shot a huge stream of cum into the air.