My mother died in a freak accident when I was around six years old, my dad was devastated, but two years later he found someone else, Lauren who was a single mother her daughter looked just like her mother Cassidy was just six when we met.
Hello my name is Nathaniel but everyone just calls me Nate, I'm 18, I'm about 6'3" I have light brown hair with green grey eyes I weigh about 180lbs, I have an 8" dick.My step sister is Cassidy everyone calls her cassi or Cass, she is 16, she's about 5'7" with maybe 32 C boobs, she has blond hair with bright blue eyes. She weighs 132 lbs.
My father and I have been planning a surprise for my step mother Lauren, it's their 10 year anniversary, and dads planning to take her on a cruise for a week, I'll be looking after Cassidy.
Before they were set to leave I was given a list of things to do in an emergency, where everything should be, you know, all the stuff parents do before they go out, given lots of hugs and kisses, they told Cassidy to do everything I told her because I was in charge. As they were leaving we waved goodbye, 'lets go inside and I'll order us some pizza and a movie' I said, she said 'sounds great!' And skipped inside.
After dinner we decided to watch another movie, and when that finished we both went to bed. The next morning I had to take care of my morning wood and shower so I got my towel and walked to the bathroom beside Cass' room as I was passing I heard I small whimper, I thought she was in pain, I stood there listening, I heard another whimper and decided to check it out.
I turned the door knob as slowly as possible as not to disturb her, and soundlessly pushed the door open slightly, and the sight before me nearly bring me to my knees, there was Cass on her bed with her knees spread open so I could see her glistening pussy, I nearly came from the sight of her slender fingers sliding along her folds, I looked down at myself and saw my dick in my hand 'how did that get there?' I wondered.
I looked back at the sight before me and my hand automatically started pumping on my rock hard erection, I heard a low moan and realised it came from me, I heard Cass moan and whisper fervently 'ohh yes Nate, just like that, I love it when you fuck me uhh' my hand was working furiously on my cock, I wanted to cum with her and she looked close to cumming. We stiffened up at the same time, her back arched of the bed and my knees buckled as I fell to the ground with my cock spurting out my jizz onto the door. I recovered and cleaned the door and stuffed my now flaccid cock into my shorts and closed her door and finished making my way to the shower, in the shower I jacked off one last time to the images now burnt into my mind, after I cleaned myself up again, I thought 'I'm going to go to hell, who thinks of their sister like that?' I felt physically sick of myself. I avoided her for the rest of the morning feeling like the biggest sicko for doing what I did.
When lunch came I couldn't avoid natures call anymore, I was also terribly hungry, so I snuck out of my room trying to avoid her for longer so she wouldn't see the shame and guilt on my face, but when I got to the kitchen there was a note on the counter addressed to me, it read 'I'm going to hang out with some of my friends, I'll be home before dinner love Cassidy xx' I was overwhelmed with relief, she wouldn't know but I will so I decided to make her a special dinner, I got in my car and made my way to the supermarket.
When Cassidy came home dinner was coming out of the oven, I told her to sit at the table, she went to sit down and I asked her how her day was she said 'it was fine, what's with this?' I said 'nothing, I just wanted to make something nice for dinner' as I set the food on the table. We ate and talked about nothing in particular.
Then the topic of girlfriends came up, 'so is there anyone special, you know, a girl?' Cassidy teased, I said 'nah, you know there's no one I'm interested in now, what about you? Any guys I need to beat up?' She giggled 'AS IF! You know I'm not interested in anyone either', 'alright, do you want to go find a movie to watch while I put everything away?' I asked, 'sure no problems' she replied.
The movies she picked was a scary one, so we got a blanket and snuggled up on the couch, during a suspenseful scene, she got even closer and jumped when the guy was shot, basically sitting in my lap, I thought 'oh no! I hope he doesn't wake up' but of course no sooner as the thought finished he started to lift up, so I shifted so she wouldn't notice, but that just made it more noticeable, she squealed 'what is that?!' I jumped up, my shorts tenting, as she ran from the room the hers, I ran after her, as she slammed the door in my face, I told her desperately 'I couldn't help it!! When a pretty girl sits on my lap I can't control it, I'm sorry!' 'Just leave me alone!' Was the only response, so I went to my room and after countless hours I finally fell into a restless sleep.