I had never had any sexual thoughts about my sister at all so I did not want to be naked around her for that reason. I guess I was just a nudist at heart, and she was the only one I could share that with.
It all started when my twin sister and I were 15. It was sometime during the summer so it was just her and me at home all day every workday (Both of my parents work). Sometime in the beginning of July, there was a heat wave and our old air conditioner couldn't keep up. The house was hot as hell...pretty much literally. I hated sweating in my clothes in my house. So I had an idea: try out nudism in the house when it was just my sis and I. I guess most people would've just stripped down to underware or something but I skipped that stage (I don't think I even had thought of just doing that).
So one day I woke up and decided that that day would be the day I'd go naked. I got out of bed with my morning woodie and went to the bathroom. I let my dick go down (no jack off just natural deflation), and then walked around the house (still clothed) to make sure my parents were gone and it was just me and my sis. I got to the kitchen and ate breakfast with my sister who had woken up a little bit before me. We talked like usual and then went to our seperate ways. She went to the family room to watch tv and I went to my room to get ready for my morning shower. I got to my room and stripped entirely. Then I got a towel, slung it over my shoulder, and walked to the bathroom to take a shower. This was all upstairs so my sister hadn't seen me naked. In fact I sometimes did this when I wasn't playing nudist because I knew she wouldn't see me. After my shower, I dried off in the bathroom and then walked out entirely naked. I walked downstairs and went into the family room and sat down next to my sister who then looked at me and her mouth dropped. Here was her twin brother sitting next to her entirely naked.
She said something like: 'Nate, what the f*ck are you doing?' All the while staring at my soft dick.
'I'm just hot so I decided this would keep me cool' I replied.'You don't mind do you?'
'Of course I do! I dont want to see that!' (pointing to my dick).
'Well, you've seen it before when we were kids...it just was not this big and hairy.'
'Fine. Whatever. But put clothes on before mom and dad get home.' I said something like 'Duh I'm not stupid.' So for the rest of the day until our parents came home I stayed naked. That night, I went to sleep without any clothes on, figuring my parents wouldn't see because they never come into my room at night or early in the morning.
I woke up the next morning with wood again. I got out of bed and walked into the hall headed for the bathroom. As soon as I walked out of my room, my sister walked out of the bathroom and her eyes went straight to my hard seven inch dick which was pointing straight at her. She immediately yelled 'Ewww, NATE!'
'What?' I said, 'You saw me naked all day yesterday.'
'Yeah, but you weren't hard!'
'Ever hear of morning wood, sis?'
She just stared in awe as I went past her into the bathroom and decided to give her a show and not close the door to piss (after all she had already seen everything). I forced my boner to face the toilet bowl and let out a nice piss. At the end I shook it a little extra for her enjoyment. I then washed my hands and invited her to eat breakfast with me. Sometime during breakfast my boner disappeared. I then told her I was going to shower and she demanded I wait until she brushed her teeth. I reminded her that I didn't really care if she was in the room while I was showering. She said 'O yeah. Okay.' So I went upstairs and hopped in the shower. A minute in I saw her walk in and she waved hi as she started to brush her teeth, looking at me through the glass door using the mirror. When I got to washing my dick and balls, she was still there. Somehow I started to harden up and she definitely saw that. Even though she finished brushing her teeth before I finished my shower she waited for me and we kinda chatted until I was done. When I turned off the water I started to dry off. When I got to drying off my still hard dick. She said 'Aren't guys supposed to jack off when they're hard?' I said: 'If they want to lose their boner.' So she replied: 'Don't you want to? Isn't it weird to go around like that? Do you want to do it?' I asked: 'You mean here?' 'Yeah, why not? I've already seen you naked with a boner.'
I was honestly really horny at that moment so I agreed. I invited her into my room where I grabbed some lotion for lube, sat on my bed, and began jacking off. She sat on my floor staring up at me stroking my member. After a couple of minutes I could feel the cumming rising and soon after I shot a huge load that landed right in front of her. She just left with a smile and I cleaned up my carpet.
Later that afternoon my parents called to say that they were spending the night out and wouldn't be back until midnight so I got to remain naked for longer. I used the extra time to jack off some more in front of my sister and this time with porn.
We only had a couple of desktop computers in our house at the time so I could only jack off to porn when I was completely alone, but now that my sister appeared to be okay with everything I could do it more often. So that night when we were both just surfing the internet in the PC room, I went to one of my favorite porn sites. I just started jacking off to porn right in front of her. She watched carefully as I came for the second time for her. She was also interested in the porn which she had never seen.
For the rest of the summer, I walked around naked all day and she would always watch me jack off. Usually she'd either wake me up and watch me get rid of my morning wood or watch me blow a load in the shower. Sometimes I'd give her an afternoon treat too. Whenever our parents were out late we'd hit the porn.
Our birthday was in the fall and she gave me a special 16th b-day present: a handjob. She woke me up that morning with her cool hand stroking my hard cock. I remember blowing my load onto her face and then wiping it off with tissues.
Until today I have jacked off for her or she has jacked me off at least once a day. I have never seen her naked or asked to. I'm okay with just having her there to get me off.