When my dad remarried a few years ago, I not only gained a step-mother but also a step-sister. It was very weird having a girl in the house that was the same age as me. Before my father's new union my only sibling was my brother and he lived with my mother, so I was not used to sharing the attention. Worse yet was that Lisa was one day older than me so I was not even the oldest anymore. Just when it was beginning to look like having a live-in sibling was going suck, I learned that having a sister could be a great thing.
She and I were both eighteen year old seniors as we both started kindergarten late. All of Lisa's friends were eighteen and some were even a little older. During our senior year she and I became pretty close and I would regularly express my interest in a certain one of Lisa's friends and low and behold that very girl would spend the night at our house and she and I would hook up with in the space of a couple of weeks of my mentioning my interest to Lisa. Now I was of course suspicious as to why my step-sister would let me sleep with her friends, but hey I wasn't going to question it.
When our parents first got married Lisa was short and chunky, but in the space of three years she has lost the baby fat and grown a few inches in height. Lisa has grown into a nice looking young lady. Her long blonde hair and green eyes, along with an incredible ass and long athletic legs made her by far the prettiest girl in our school. Shortly after she and her mom moved in with my dad and I, Lisa made two new friends, one was my cousin Becky and the other was her boyfriend Andy. Andy was a year older than us and a complete geek and by the time Lisa hit 18 she was way too good looking to be with the likes of him, but they had been together so long that she did not care. She said she loved him and she would not leave him. Well shortly after our graduation, Andy dumped Lisa for a band nerd and Lisa was devastated.
That dickhead dumped her right after the graduation ceremony and being a good brother I skipped the post ceremony parties and stayed at home with Lisa. I bought some alcohol to help her dull her sorrows and mine since I was missing the after graduation parties. She cried for hours and drank a ton of alcohol. It wasn't long before she was totally wasted and started asking what she had done that was so terrible and was she that disgusting and ugly and all the other things that teenage girls ask themselves and others after a breakup. I sat with her on the couch in the sitting room in the basement of our house and tried to comfort her as best I could. I could not believe that I had given up a night of parties and drunken sex and I started to seriously regret my decision to stay home with my sobbing sister. At some point I must have given away what I was thinking because Lisa looked at me and told me how nice I was for staying with her and then she gave me the answer to the question that had been bugging me for most of the school year.
"You don't have to do this to pay me back you know" Lisa said to me. I turned and looked at her for a minute and finally asked her what she meant. "I'm sure by now you noticed that all the girls you liked always seemed to spend the night here, well that was my idea." I was not really sure what to say to her and all that came out was a lame "thanks!" Lisa smiled slightly and told me that she had selfish reasons for setting me up with her friends. I watched as her face turned red and she looked at the floor and my head reeled as she began to explain. "I used to watch you do it. I liked you but I thought you wouldn't do it with me since I was your sister and I thought that watching you was about as close as I was going to get. So I started inviting girls over that I knew you liked so I could watch you do it and masturbate. I kept on doing it because I would always have the best orgasms while watching you with my friends."
I was a little stunned. Not only had I just learned that my step sister used to finger herself while watching me screw her girlfriends and that she had her best orgasms while she was doing it, but also that she had set the whole thing up for her own pleasure. The implications of this whole thing were not lost on me despite the fact I was pretty drunk and I started to think that this night might not be a waste after all.
I put my hand on her knee and said "Lisa, I wish you would have said something a long time ago. It's not like you are my real sister or anything."
Lisa looked at me, leaned over and kissed me, tentatively at first but when I didn't push her away she got more aggressive, putting her arms around my neck and climbing onto my lap. She began to grind herself against my steadily hardening dick as I reached behind her and unhooked her bra with much practiced efficiency. Then I lifted up her shirt and briefly breaking our lip lock I pulled her shirt and bra up over her head, exposing her firm breasts. As she leaned back in to reconnect our lips, I let my hands wander to Lisa's breasts which weren't big, a little bigger than a baseball, but they were definitely firm. I rubbed her breasts in a circle with my palms as I tweaked her nipples, causing her to sigh through our kiss. Lisa stopped our kiss and she pulled off my shirt and unbuttoned my pants. She then started on my zipper and as she pulled it down my cock got some partial relief from the confines of my pants leaving only my boxers barely containing it. Lisa leaned forward and started kissing me again as she drove her hand into my shorts and wrapped it around my dick.
