I would have never expected my sister to do this...
My sister was 18 when this happened, and I was 15. I had always found my sister to have an amazing body. She has small boobs (but not too small) and is medium height, as well as blond hair down to the top of her back. I have spied on her a few times when she has gotten out of the shower, and have found out that she shaves her vagina. Anyway, onto the event...
I had always been turned on by the thought of getting caught masturbating. Not by my mom, nor my dad, but by my sister. I came home from school one day to find I was home alone. I decided that it would be a great time to relieve some stress from school and masturbate, so I went up to my room and reclined on the bed. I hadn't gotten that much into it when I heard my sister come in the front door. Yes, I heard her. I knew that she always, and I mean always, goes straight to the bathroom when she got home, and in order to get to the bathroom you must pass my room. I chose to set it up so she would catch me.
I heard her feet coming up the stairs. My heart pounded as I adjusted my speed so she could see my entire cock better. It wasn't too long now, she was almost to my room. I closed my eyes and started breathing heavily. All of a sudden, I hear my sister gasp and say 'Oh my God..'. I opened my eyes and looked at her, still stroking my cock. She apologized and went to the bathroom. Darn, I thought, I wanted her to join or help me. I finished up into some tissues, threw them away, then got onto the computer to play some games. But, I was interrupted by a knock at my door.
My sister walked in and sat on my bed. She wanted to say sorry again and that it was normal for guys to want to do that. I said thanks and asked her to please not tell our parents. She said that she wouldn't. I then broke the silence by asking if she ever does that. She said that she never had. She stood up and motioned me over for a hug, so I walked over to her and hugged her, my body pressing against hers. Right as my arms went around her, I realized that my cock was pushing into her crotch, and this immediately got me hard again. I knew for a fact that my sister was going to scream at me. But, she didn't. To my surprise, she softly started to grind onto it. We stopped hugging, and at that moment, I kissed her. Tongue and everything. She kissed back while she continued to grind into my cock.
She then shoved me onto my bed, pulled my pants down, and asked if she could give me her, and my, first hand job. Of course I said yes. I felt her hand slowly grasp my cock and she started stroking up and down, very very slowly. I was so horny though, and I actually came after about six strokes. I shot all my cum, some on her lips, a little on her chin, and some onto my stomach. She licked her lips, gave a satisfied 'Ahhhh', and stood up. She said thanks and told me to listen around midnight. I wasn't sure what she meant, but said alright between heavy breaths. She then kissed me again and left, leaving me to clean up the mess.
Later at midnight, I was sitting in my room when I heard breathing. I listened more closely and could hear little moans and squishing noises. It was obvious that my sister was masturbating to the thought of what had happened earlier. I got hard right away and masturbated again, but to the sounds of my own sister masturbating.
This continued on for a while, exploring each others bodies and what-not. But, that's for another time. Now, I have to go stroke myself because just writing this got me extremely hard. Hope you have a great cum reading this story.