When I was 15 and my sister was 13 I started to sneak into her room at night. At first I just masturbated onto her legs or feet if the were exposed. Then one summer night she had kicked off her covers and I climbed onto the bed and rubbed my penis on her until I shot my load on her legs. After that I was hooked and practically every night I would sneak into her room and rub my dick on her until I came. Many nights I did this two and sometimes three times.

Only a few times did she wake and I had a stupid question I asked to cover me.

I got bolder and was now rubbing my cock on her thighs and sometimes on her panty clad butt. On a few occasions I slid my erection under her panties and rubbed my cock in the crack of her ass until I blew my load of hot cum.

I fingered her a few times, but I stopped when it made her wake up. I knew that this was wrong but the impulse for sexual release was stronger than my fear of being caught.

I remember one night I was humping her leg and I had just shot a load of cum on her thigh when the hallway light went on. My mother was using the bathroom in the middle of the night. If she had opened the door to check on her daughter I would have been caught with my semen on my sister's leg.

You can not imagine how powerful the orgasms I had while lying on my sister's bed with my cock pressed against her warm skin. This went on for two years until I went away to college. I must have cum of my sister's bare skin over 500 times and as far as I know she never found out and I never got caught.