It felt so natural
My sister and I are both in our early teens. Our bedrooms are in the basement of our parents house and we share a bathroom between us. Normally she gets up before me and showers and gets out of the bathroom before I even wake up, but one morning I woke up and had to piss so bad I couldn't hold it. I made my way to the bathroom and could hear the shower running so I knocked on the door. My sis asked what was up and I told her I had to piss bad and didn't think I could make it upstairs to use the other bathroom without pissing myself. She laughed and told me the door was unlocked and to come on in.
I opened the door, and could see the outline of my naked sister behind the shower curtain. I had always thought she was beautiful, she was kind of short and a little heavy, but not really fat, just an average girl I guess. She had just started to grow some really nice boobs, and a nicec round ass, and as a teenager, often found myself fantasizing about what they looked and felt like, but of course she was my sister, and I was taught that it was not ok to think that way.
She poked her head out from behind the curtain and smiled and said " you won't peek, will you". I replied "not if you don't". She grinned and closed the curtain. I immediately dropped my drawers and started taking a massive wizz into the toilet. At that point, she turned off the shower. "Jesus little brother" she said. "Sounds like you've got a fire hose going over there". "Hey", I replied, "I told you I had to pee bad" . After what felt like a five minute piss, I pulled my boxers back up and turned around to leave. I was startled to see my sister standing directly behind me, and let out a quick yelp. "Holy shit, sis, you scared the shit out of me" I said, "what are you doing?" She was now standing directly in front of me, with a towel wrapped around her. She had kind of a nervous look on her face, but she forced a smile on her face as she pulled off the towel and let it drop to the floor. I was momentarily awestruck as I gazed upon her naked body, almost paralized, I could do or say nothing, I just gazed at her perky tits and erect nipples, and then I looked down and saw the most beautiful, clean shaven pussy I'd ever seen. My 6 inch cock immediately became erect as my sister threw her arms around me and started kissing me on my lips. Neither one of us said a word as she took my hand and led me into her bedroom. I made beautiful love to my sister that morning, and it felt like the most wonderful, natural thing in the world. We have done it many times since, and are both very happy with our relationship. We have no idea why some people think this is wrong, as long as both people are willing, it has made us closer to each other than ever before.