4 months ago, my sister and I were lost at sea. I had invited my sister, Lily, to a cruise with me across the Pacific. She and I had needed a vacation for some time; I had been working full-time as a botanist in Colorado and she went back to college to get her PhD in zoology. After taking some time of convincing her and making time in both of our schedules, Lily finally agreed to go with me. The trip was supposed to last ten days, most of which was supposed to go up and down the west coast - from Cali to Mexico to parts of South America then back again. 5 days into the trip, we hit a rough storm and our ship ended up capsized. Lily and I were so worried about making to one of the lifeboats we didn't have time to look for other survivors.
We washed up onto the shore of a little island far from the main land. We quickly realized that we were the only people on that island. Our first week there was spent trying to make signal fires, finding food and fresh water, and trying to find a place to sleep at night. Lucky for us, there didn't seem to be any predators on the island, a few foxes here and there but nothing that could eat a human. My time as a botanist worked wonders for me and my sister as I could identify which plants were safe to eat and harvestable. Lily would spend most of her time setting up lures and catching rabbits. We built a shack to shield ourselves from the elements and waited for someone to come rescue us.
After 4 months on the island, we gave up all hope of ever being rescued. By then, we had food, water and shelter. We kept ourselves busy at first, building more signal fires and whatnot, but we eventually got into a rut. Something was missing and we both knew what it was. 4 months of living with each other, neither of us had much of a chance to "release." I had time by myself to jerk off every now and again, I just assumed Lily did the same when I wasn't looking. But that wasn't enough. Without ever talking about it, we both knew it would happen sooner or later; my sister and I would have sex eventually.
One day, after finishing my daily chores, I went to take a bath in one of the nearby springs we used to bathe. When I arrived, I saw that Lily had already beaten me to the punch. Normally, I would have just waited until she was finished. But something was different, she looked different. I had been so pent up for so long I just stood there and watched as Lily washed herself. Her pale skin, her perky tits, her supple ass, that crinkly red hair, everything about her was just...perfect, beautiful even. Unconsciously, my hand made its way toward my now fully-erect cock and I began stroking. I don't know how long I had been standing there watching her. Minutes probably, but it felt like an eternity.
Lily turned and saw me standing there staring as I stroked. Normally, she would have screamed at me and told me to leave, but she didn't. Instead, she stared back and watched me. Just like me, almost unconsciously, her hand reached down to her crotch. The two of us watch each other until completion, the noises I made were almost animalistic. When I regained composure, I motioned for Lily to follow me back to the shack. It was time.
I opened the palm leave door to our shack for my sister like a gentleman. My eyes were locked onto her as she walked past me. At this point my pants were already off, I had left them back in the trees where we were. For a moment, we made eye contact and just stared at each other. Without words, we were shoving our tongues in each other's mouths and we dropped to the ground with me on top of her. I fumbled to place my cock at her entrance as we kissed. Once I was inside, Lily finally made a noise, a shriek of sheer ecstasy. I took my sister fast and hard. "I love you." I said as plunged myself back inside her. I ended up coming inside of Lily in that moment. We both knew it was wrong. We didn't care. We didn't want to stop. I ended coming inside of her five more times in all sorts of positions that day.