I had always noticed and longed for my sister's body. She had C-cup breasts and a nice big ass. When this story started I was 15 and my sister was 14. My sister just started having her period and was starting to ask questions about sex. Our parents were always at work and it was summer break. All of our friends were on vacation so she had to ask me. She asked if sex was dangerous and I told her there were some diseases, but she wouldn't have to worry about them unless she had sex with someone who had it. She asked if I'd ever had sex. "Of course" I said. She asked if it felt good and started to blush. I told her it was the best thing in the world. She asked if I would show her how to have sex. I knew it was wrong but she is so hot. Then she asked if she could get pregnant. At the time I didn't know that she was having her period so I said no it will be fine. She started to get undressed and so did I. I couldn't stop staring at her tits and ass. I told her she looked gorgious. When I whipped out my cock she gasped. "It's so huge" she remarked. I told her that theres a couple different kinds of sex. There is oral and theres regular below the belt sex. "What is oral sex?" she asked. "It's when a girl sucks a man's penis or a man licks a girls vagina or pussy," I replied. She started blushing and asked if she could suck my penis. I couldn't believe it. I told her to go ahead and use her tongue. She started to pump my shaft with her mouth. I could feel her tongue circle my head. I started to play with her tits and they got hard instantly. I started to harden so I asked if she would swallow my cum or spit it out. She asked if it tasted good and I told her that when it went into her mouth that she could kiss me. I said that we both could try it. I started to shoot my load into my sister's mouth. She didn't gag to my surprise. When I finised, she came over to me and we locked lips. My cum tasted salty but good. We both swallowed some and took a little break. She asked what we should do next. I told her that I would lick her pussy and see if she could cum too. I started to lick and started to kick back and forth. It didn't take long for to ejaculate. Her cum tasted sweet but delicious. She told me that was the best feeling she ever had. I told her that we should have real sex now. She asked if it would hurt and I told her it would at first but it would feel better latter. She said lets do it. I spit on to my dick and made sure it had enough lube. Then I slipped my head into her pussy. There was a little screaming at first but then we got into it and eventually I stuck all 7 inches of my hard cock into her. All of a sudden she screamed and a little blood started to run out of her vagina. I didnt notice it until after I came into her pussy. "Oh shit!" I said. What is it she asked. Okay you might get pregnant. She pulled my dick out of her pussy and slapped me hard in the face. I didn't feel it though because I was blushing so much. I couldn't believe my bad luck. She asked me what we should do. I came up with the wildest idea and just told my sister. I told her that we should come clean. Our parents were really religious, so we couldn't have an abortion. My parents had well paying jobs and good reputations. I told her that they could fake our deaths and secretly take care of us in our cabin in the mountains. She asked if it would get us out of school and I said it would get us out of school and work for the rest of our lives. She started to calm down. The next day she took a quick pregnancy test and she confirmed it. She was pregnant. We told our parents about the pregnancy and the idea. They couldn't believe either one, but they accepted each one. They told everyone that we both died of the flu and that they had us cremated. They secretly moved us to their private cabin out in the mountains. Nobody knew we were there. Our parents made a catch though. We would have to take care of our child together. Our mom's a doctor so she helped my sister give birth to our child. Our parents were going to bring us supplies every week. We had a daughter and she grew up normally without any disabliities or mutations. A couple of weeks after our daughter was born I asked my sister if she liked the sex and she said she loved it up until the whole pregnancy thing. I told her that we could do anything here. We could have sex all the time and nobody would know. After ten years of nonstop protected sex we started getting really dirty ideas. Our daughter started filling out. She had pretty big breasts for her age. We had been homeschooling her and we just gave up since none of us could ever leave the vicinity of our cabin. We told our daughter about sex and she told us she had seen us doing it before. She said it looked fun and she asked if she could have sex with us. We said sure and I fucked her in her pussy while my sister made out with her and played with her tits. We basically had a life full of protected sex until we died. So our daughter could have fun I got my sister prgnant again and we had a son. It was one big incestful family.