One afternoon I was watching this movie with my sister, I’m 13 and she’s 17. She’s a very pretty brunette, 5’8″, blue eyes, and a nice 36-24-36. Anyway, as my sister and I are watching this movie, we see this couple make love on the beach. I put my hand on her leg and she’s smiling at me. I ask her “can I rub my penis on your leg?” and she says “sure”. My sister turns the TV off and we head to her bedroom, my sister closes the blinds, luckily our mom was already at work. My sexy sister takes my clothes off, then she takes her shirt off, a nice plaid long sleeve shirt with the sleeves rolled up. I get on my knees and caress my sister’s thighs. I zip down her jeans, unbutton them and take them off. My penis has gotten hard, and I’m smiling at my sister’s panties. She’s wearing a white nylon bikini with a nice floral waistband. I get her up against the wall, she gets on her footstool and I start rubbing my nice hard penis on my sister’s very pretty, silky smooth leg. I love how smooth and silky my sister’s legs are. She has her head up and her eyes closed as I’m rubbing my penis up and down her leg, she looks so sexy. After rubbing my penis on my sister’s leg for a good 15 minutes, I begin to ejaculate my pure white semen on her thigh. My sister brings her head down, opens her eyes and say softy say “oooo, you’re the best kid brother a girl can have”, then we kiss.