One night when we were watching a movie, my twin sister decided to get very snuggly. My parents were out so it was just the two of us sitting on the couch snuggling watching some movie I don't remember. At first it was normal stuff. But then I felt her shift and her boobs became pressed against my arm. It felt like it had to have been intentional. I think she was literally pressing them down onto my arm to be seductive and it was working. I started to get hard almost instantly, especially because just an hour beforehand I had been reading incest stories on here but hadn't gotten off. So my balls were full and I was horny.
I let the situation be for a little while as she continued to press her firm tits against my arm and her head seemed to caress my chest and shoulder. I wondered if she could see my boner which was partially tenting my shorts but not too bad because of the way I was sitting and the direction it was facing. After a while she got up and paused the movie saying that she had to go to the bathroom. When she entered the bathroom I took a moment to rearrange my package so that my boner was less obvious. When she walked out she suggested that I also use the toilet so we wouldn't have to stop the movie again. I agreed and stood up to walk toward the bathroom. As I did so my boner snapped out of his position into one that really tented my shorts and my sister saw. She kinda smirked as I scooted past her pretending nothing was wrong.
By some miracle I softened while taking a piss. I walked out of the bathroom and my sister said 'No longer turned on huh?' I was kinda embarrassed but I brushed it off. After a minute of continuing the movie she got back into her boob on my arm position. I of course got hard again. This time it was more obvious. She must have seen as she slowly moved her hand toward my crotch. She stopped moving for a minute and seemed to be watching the movie so I took the chance to rearrange my dick by putting my hand into the top of my shorts. As I withdrew my hand I felt hers brush past mine. She started caressing my hard dick and after just a minute I started cumming in my shorts. I could feel my sister rubbing her cummy hands against the inside of my boxers to clean them. After that she withdrew her hand and gave my softening dick a squeeze from the outside. I was still in too much shock to do anything.
We sat there, me drenched in cum below the waist, until the credits came on. At that point my sister said: 'You gonna shower or just sit there wet all night? You're a mess...maybe I should help you.' She dragged me toward the bathroom and got the shower running. She instructed me to undress. I was like : What the...No!. It still hadn't quite sunk in that my twin sis had given me and handjob...just randomly! She goes: But look at you! She started to unbutton my shorts and yank them down leaving me in soaked boxers. I saw myself in the mirror and the entire front of my blue boxers were dark as I'd ever seen them. The inside of my shorts were also pretty cummy.
The outline of my hardening cock became apparent in my wet boxers and I instinctively stuck my hand in and started rubbing. My sis said: 'Again? Ok.' She deboxered me and replaced my rubbing hand with hers. She knelt in front of me and made me cum after a minute. I shot a load onto her face and clothed tits. She said that she had better join me in the shower. So she got undressed too and we hopped in. We started washing each other and I randomly started grinding my soapy dick against her stomach. It didn't take long for me to cum again, this time just leaking a bit of cum which got caught in her pubic hair. I then fingered her to a great orgasm.