Brother and Sister home alone turn into Brothers fantasy

It all started on night when I just needed to get laid. I was the horniest eighteen years old you have ever met. It was an unsuccessful Saturday night so far, my parents were out of town and the only ones home were my sixteen-year-old stepsister and me. I always thought that she was one of the hottest girls that I knew. She had the brunette with blonde highlighted hair that was about shoulder length, tiny little shoulders, a perfect set of 34C size tits. A flat belly with a belly button ring that she showed off to everyone, this ass that brought me to tears and legs that made her stand about 5’4. 

I have been infatuated with her for as long as I can remember. I used to spy on her through the window. I think sometimes she knew that I was there because she used to take extra care of admiring her body in the mirror that was right in front of her window. I would run to my room and jerk off leaving the door open hoping that she would walk by. I used to fantasy about her walking by and peaking in my room and see me rubbing my 7-inch dick. See would step into the room and slowly rub her pussy through dress then she would begin to get a little more bold and slowly lift up her dress and slip a finger around her thong and into her wet lips. Playing with herself and switching fingers long enough to taste her own pussy juice. Then she would slowly approach the bed wanting so badly to touch me and would bend over with her ass in my face while she continued to play with herself and begin to slowly stroke my dick and then when she could not take it anymore she would move her month closer to my dick and then begin to move up and down on my shaft until I exploded in her mouth. Of course that never did happen like that. But I did make my dream come true. 

She had just broken up with her boyfriend and had nothing to do and we decided to hang out together that night. I asked her what she wanted to do but she did not care as long as it included the consumption of our parent’s alcohol. I did not care as long as I got a chance to see her naked. So I said that we would make it a date. I was off to take a shower; change and then we would hang out after that. I ran into the shower and started to jerk off. The thought of drinking all night with my sister streamed endless fantasies about getting her drunk and fucking her. As I stood in the shower fantasying about this I heard a knock on the door. 

“Yes?”
“It’s Rachel can I come in”
“For what?” I asked rudely
“To help you jerk off, what do you think, I need to go pee”?
I could not believe she just said that. I stood there in the shower not being able to talk. 
“Hello” I heard again.
“ Ok come on in, but I am not promising that I will not watch” I said.
She laughed as she entered the bathroom I poked my head out of the shower. She walked in wearing a short pair of shorts with the words ‘Sexy’ printed across her ass and a white tank top with no bra. And it was obvious with her nipples showing through that she was I bit excited about peeing while I was in the room. 
“Hey” I said.

She did not say anything and began to pull down her shorts. I could not believe she was about to take off her shorts while I was standing there staring at her! As she lowered her shorts I began to she the beginning of nicely trimmed hair when she looked up.
“Do you mind?” 
“No do you?” I asked.
We just stared at each other for a second. No one seemed to want to say that they did. Finally the silence was killing me.
“Fine” I said and turned my head back into the shower. I could not believe she was wearing that outfit and had to pee 2 minutes after I got in the shower. 
“What are we going to do tonight?” my sister asked me.
“I thought that we were drinking?”
“But what else?” she asked.

What I wanted to answer this question with now. Especially because as she was asking I was holding my dick in my hand. 
“I am sure we will cum up with something” making sure I slowed down to say cum. 

I thought that it maybe a good time to sneak another look. I slowly poked my head from behind the curtains. At this point she was looking in the mirror at her ass. Trying to see if it was shaped perfectly which is was. As she slowly ran her hand down her ass she slide it right down the crack of her ass and running it along her mound. I watched her in amazement she was so hot. I prayed to god that she would continue to run herself long enough to let me finish what I was doing. 
She must have gotten a sign from God because her other hand slowly pulled her shirt up enough to reveal part of her tits enough to see one of her nipples sticking out which was so hard looking. My sister starting twisting and pulling on her nipples then she quickly slide her hand down the front of her shorts. She started to slowly rub herself as I watched I opened the curtain a little more to get more room. She continued to rub herself in the mirror and she must have gotten close because I could hear her start moaning. She was now making smaller circles around her pussy lips. She switched her hands and slowly put one finger in months and sucked the pussy juice from it. I was living out my fantasy of watching my sister play with herself right there and nearly fell out of the tub. 

She must have heard me and without taking her hand out of her shorts quickly turned towards the shower. I do not think she thought I would be there staring at her with my dick in one hand. She stared at my dick for a second then realized she still had her hand down her shorts. With that she pulled her hand out of her shorts and ran out of the bathroom. 

I did not know what to do or say.
I knew one thing that wow if nothing else happened that impression would be burned into my memory for the rest of my life.