I have three sisters. We are all spaced two years apart, with the youngest, Rachel, a Sophomore at Loyola, which is a strange choice, given that we are a Mormon family, and BYU is literally down the hill from our house. That Rachel left home for college, and that we are Mormon are both important aspect of what happened. The first gave a sense of transience to what occurred. We both knew we would be able to walk away from our actions without seeing each other to have a daily reminder. The second, that we were Mormon, meant that even at eighteen sex remained a mystery for me, because Mormons believe in chastity, and it is not unusual -- and was true in my case -- to have no sexual experience as a teenager. I had never touched a girl sexually, nor seen a girl undressed, in real life or through movies (and certainly not through pornography). I never even watched R-rated movie.
We were not even supposed to masturbate, but of course that was a bit beyond the veil. And the language I am using here, like cock and cum, is language I never used before.
But, I should add, sex was not much of a mystery to Rachel. She had monogamous relationships, but whomever she was with got to know her very well. I found out from her later, once we became open about everything, that she would let her boyfriends have anal sex with her because they believed that if they didn't enter her as God intended it did not reflect a loss of virginity. One reason she did not go to BYU, or even the University of Utah, was not so much because she was looking for a more intense educational experience. Loyola is an OK school, but it didn't have anything on BYU educationally. What it did have, and what almost any school had, was a more open sexual and party culture. And that is what Rachel wanted.
Where to start... I think it is the point at which I became to think of my sister in a sexual context, the point where she became a target for my sexual urges. This happened on her first night home for the Christmas break. We were talking in the TV room about her last semester. About what I should expect when I went to college -- for me, that was BYU. She was sitting on our leather couch and I was in a chair facing her. She sat cross-legged, and her nightgown inched up so I could see her hair. It was only for a moment and she didn't seem to realize that I had this view, but without thinking rearranged herself. For a hormonal teen who had no first-hand knowledge of what lurked down there, this was enough to excite me. I became hard in a moment. I hoped she didn't notice, but as things progressed over the next while, I suspect she had.
I would think about seeing her again. It occupied my thoughts. I would masturbate thinking about getting my cock to rub against her hair, then as my mind released the natural inhibitions of fucking my older sister, I fantasized about her sitting up on the couch, and me entering her. Watching my cock move into her. Not responding with moans or movement, but rather imagined her observing it with detachment. I could go no further with my fantasy; I could see her as an object with a vagina to penetrate, but not as someone who would engage with me full-stop.
And, strange and perverse to me at that time, I started to enrich my masturbation sessions by taking her used underwear from her closet floor, fanaticizing that I was pushing them to the side and going into her. Then I would put them up to my face and pretend my face was between her legs. At first I felt ashamed at doing this, but day-by-day it became more natural. I would look for a pair that was stained, and that had the strongest scent. I would be wrapped up in the seconds before I came and press the underwear against my nose, being excited by what I basically felt even in the moment was a disgusting activity.
As one thing -- seeing her hair -- led to the next -- her used underwear -- that led to a third, and the one that became decisive. The inhibition of fucking her as a female (she is my sister, so I wouldn't say woman, and I also can't say girl), as the possessor of a vagina, and of having her seeing me as a cock, receded. I really wanted to fuck her. My teeth ached when I saw her, and this urge didn't subside even with jerking off. I would get erect spontaneously around her, and the bulge must have been evident to her. I hoped she would see it. But she seemed oblivious to it. Maybe she took spontaneous erections as a fact of life, whether her brother or not.
When she was out during the day. I took her underwear and went into her bed to masturbate, pretending she was there with me. I had the scent of her more fully, and of course the only thing that was missing was her body. I took a towel into the bed to catch my cum, and returned the bed to pretty much the way I found it; not too hard to do, because she never made it.
Maybe I did it accidentally, or maybe subconsciously I wanted to leave my semen there to be pushing against her as she slept. In any case, one time when I squirted out, some shot beyond the towel and wet the sheets. I didn't notice it, but that night she did.
We sat in her room, talking, her nightgown now properly draped. She opened her sheets and saw the streak from my cum. She had undoubtedly navigated around the post-coital wet spots, and knew what this was. She looked at me almost like she could not process what must have occurred. She tried to continue with the conversation, but after half a sentence asked, in a voice that did not change, "Did you go into my bed to masturbate? Did you ejaculate there?" I'm sure she normally would say "did you jerk off" and "did you cum there", but felt she needed to be more proper and clinical with me.