Costume Sex

When I was nineteen, my family went to a costume party. I had always thought those were lame, and I wasn't looking forward to wearing a costume. So I was going to hide somewhere and wait the party out. But when we got to our friends house, there was already a ton of people there. It looked like the whole neighborhood had shown up.

I groaned inwardly and went inside with my parents and my older sister. She was two years older than me, and was kind of a health nut. She was always watching what she ate, and she had the best body I had ever seen because of it. She was wearing a huge tiger suit costume, and it was way to big for her. It was supposed to be a two person costume, but her boyfriend had bailed last minute. I wore some stupid alien costume that was ripped in the first few minutes of the party.

My sister, Ashley, found me sitting in the corner, knocking back a beer I swiped when no on one was looking. She had a drink in her hand, too. "Hey," she said. "What are you doing all the way over here?" I shrugged. "Just waiting the party out." Ashley looked at my ripped costume then smiled. "You wanna have some fun? Get in here and help me with this costume." I was a little surprised, but I was never one to turn down intimate contact with hot girl, even if she was my sister.

I pulled the zipper down and saw she was only wearing bra and panties. She must have remembered what she was wearing, and said "Oh, yeah, sorry. It's really hot in here. You might not want to wear your costume either." I paused, then pulled it off and stepped inside. I was only wearing boxers now, and was a little nervous. The suit was tight, and I was pressed against her. My dick was right against her ass, and I was incredibly turned on. We walked a few steps, and then she stopped. I realized why when I felt that I had an erection and it was pressed against her ass, with only my boxers and her panties between it.

Soon, we were drenched in sweat, and her underwear slid down, and it had little bows on them, which caught on my boxers and tugged them down as well. I froze, not knowing what to do. Here I was with my hard dick pushed in between my sister ass-cheeks.Suddenly she giggled, and pushed back against me, burying my dick further in her ass. I felt brave as I thrust my dick further up her ass, and began sliding it up and down, slowly at first, then faster and faster. We were by a wall, and she braced her hands on it as I thrusted in and out of her ass. She moaned as I continued to thrust as I grunted and ground my dick in her ass, nestling it firmly between her cheeks when I shot my load. She whimpered and turned in the limited space and dropped her head to my cock and began sucking me.