My step sis was with me on vacation for the entire week and our parents were gone. I saw her in her room and she only had her panties on and a huge t shirt. I couldn't help but get hard and stroke my cock. I tapped it on her ass one time and I was throbbing. I did it again and again. I thought she was going to freak out. She slid her ass closer to me and rubbed it against my cock. I couldn't believe what was happening. She finally told me to rub my cock on her pussy. It accidentally slipped in a little bit. She liked it though and told me to keep going. Finally, I fucked my hot big tit step sis until I came all over her tits.