My First Time Fantasizing About Sis

I started masturbating young. Real young... as in I cannot even remember an age where I did not jerk off several times a day. So even as a young teen I was starting to get a bit jaded and bored of my usual wank material, which as this was pre-internet was usually some combination of Playboy or Penthouse centerfolds from my dad's stash and/or fantasizing about whatever girl at school I happened to be smitten with at the time. At some point I discovered that the letters section in those Penthouse mags was really hot and simply reading those stories while wanking made me cum hard. Even harder than looking at the centerfolds if it was a really hot story. But there was one story in particular that really sent me into orbit. This one was told in the first person by a young man who had a sexual relationship with his sister. It started with them both experimenting as young teens... I'll show you mine if you show me yours type stuff. Then it progressed through the years as they shared all of their first experiences together... mutual masturbation, oral, vaginal and anal intercourse, even threesomes with others. It ended with them moving across the country to a city where nobody knew them so they could live together as husband and wife. To this point I had never even once thought of my own sister in a remotely sexual way, but it was not difficult to imagine me and her as the subjects of that story. A lot of the smaller details in the story... the ages when it all started, their family circumstances, his physical descriptions of them both, were eerily similar to me and my sister at the time. What this fantasy did to my cock was nothing short of amazing. I'll never forget the first time I read that story. Not more than a couple paragraphs in and I was already throbbing hard, my cock seemingly an inch longer than it had ever looked before, leaking precum dripping down the head. I could barely touch it for fear of cumming prior to reaching the end, which was supremely difficult since this was a relatively long story which took about 15 minutes to completely read. Come to think of it this was likely the first time I had ever edged as opposed to simply stroking as hard and fast as possible and cumming right away. By the time I finally made it to the end of the story I was literally trembling. The rush of jerking off to something as perverted, as taboo, as my own sister was overwhelming. At that point I set the magazine down, laid back on my bed, closed my eyes, grabbed my cock, imagined what my sister's naked body must look like and immediately exploded all over myself in what to this day is one of the most powerful orgasms I've ever experienced.