As a starter, this happened when i was 13.... going through puberty and had a bunch of hormones running through me. So i live in a basic family.. quite normal...But as i hit the age of 13. i realized how attractive my sister was.. (before this i had only been admiring her friends), she was actually extremely attractive, medium-tall height, brownish blonde hair... nice body.. and other nice "things" if you understand what i am saying. The week that this "thing" happened i had been thinking about her alot. I understand this sounds EXTREMELY out of the ordinary but my father at the time.. was a dentist... so he had many "tools" and equipments.. but one thing he had, i noticed, was nitrous oxide.. which i knew you use to numb people when you are operating on them, as i spent alot of time around my father's office. So that week i was thinking about my sister a lot.. i decided.. to steal some nitrous oxide.. which turned out to be a hard task because he had them in the big tanks.. but one of them would be managable for me to carry as i was 13 and could pull my own wieght. Here's the part that made this whole thing possible.. my house was attached to my father's office.. from the front of our house it just appeared to be a dentist's office. So, i had stolen the tank one night.. quite late in the night, and i carried it into my sister's room. At the time.. i was only going to use it if my sister started to wake up while i was "frisking" her, for not wanting to use a more sexual term... But then i thought about if she woke up instantly.. what would i say? soo i took the nozzle and pointed it around her mouth and sinus area. And i let the nitrous flow. I made sure not to let too much into her face.. as i knew it can be extremely dangerous.. After this i hid the can behind my sister's door... and smacked her face a few times to make sure she was completely knocked out.. Then i began to unclothe her.. when she was completely naked i began touching her breasts and vagina. i began to get really horny.. and i thought to myself, " i have already gone this far, why not go farther" i didn't have any condoms on me, so i decided that i would just pull out when i thought i would cum... I put my penis into her vagina and began moving it back and forth... at this point, for a few seconds, i felt completely horrid at myself, then i got over it... for the next about 3 hours.. i just kept doing everything possible to her... licking her pussy. shoving my penis down her throat.. basically everthing.. To this day i am sure she doesn't know, nor does anyone, to my knowing.. And this is the first time i have talked about it since then.. i am now 22 and can't forget it everytime i talk to my sister... i regret what i did.. but it still felt natural