At the time of this event I was 15 while my sister was 16. We were your average siblings, fighting once in a while but getting along most of the time. We had gotten to the age where our parents finally trusted us to be left alone without a babysitter, so they decided to travel out of town to visit some friends of ours. They agreed to leave us two alone together as long as we didn't leave the house. We agreed, preparing for a boring day of sitting around the house.
The day progressed with both of us doing various things to occupy the time. Later in the afternoon I asked my sister if she would like to play video games with me in my room. Normally she wouldn't, but seeing as we both were fairly bored at this point she agreed. Several minutes into the game I started losing, while my sister began bragging about her beating me. Thinking this wasn't that funny I started to tickle her in an effort to distract her from the game, causing her to lose as a result. Eventually this turned into a tickle war, both of us on the ground feeling all over each others bodies. At some point my hands reached around over her chest and swiped her breasts, shaking them a little bit. I immediately stopped, hoping my sister wouldn't get too upset for me accidentally hitting them. My sister wasn't necessarily fat, but I would describe her as being 'thick'. As such, you can imagine that her breasts jiggle quite a bit.
After I stopped we both sat up, kind of looked away from each other, then proceeded to play our video game again. As we started playing the thought of her swaying breasts ran through my mind, distracting me all through the rest of the game. I kept thinking over and over what it would be like to touch them again. Even though that first time was an accident I couldn't help but want to touch them again, but this time longer. As we kept playing the idea of touching her was taking over my thoughts. I couldn't stop thinking about her. Finally I worked up the courage to ask her.
'Can I feel your boob again?'
Did I say that? Did I actually ask my sister if I could touch her breasts? I couldn't believe it once I said it.
While still playing the game she just said,
I kept playing the game as well, trying to act like it was nothing, saying,
'well, I don't know, I just kind of wanted to touch it.'
Suddenly she stopped playing and turned her head my way. Uh oh, I knew I was in trouble now. I shouldn't have said anything. I then slowly look at her, not sure what she will do.
'You really want to touch my tit?'
'Well, I guess, kind of...'
She then kind of crinkled her face, closed her eyes, and started to lift her shirt up over her head. I couldn't believe it! I just wanted to touch her over her clothes, not all the way! When she removed her top she leaned back and unclasped her bra. It dropped, letting her rather large breasts fall out. I was completely stunned.
'If you really want to feel go ahead...'
Not waiting for anything I reached forward grabbing both of her breasts. It was wonderful. I fondled them, squeezed them, everything. My sister didn't seem to really mind, she just kind of sat there letting me go to work. After a couple of minutes she took my hands away.
'Ok, now do something for me.'
What did she mean? What was I going to do? Now I was just as nervous was when I asked her to begin with.
'Show me your penis.'
'Wa...what? You want me to show my...'
'Yes, you heard me. You saw my tits, so do this for me.'
I couldn't argue, and the idea turned me on a little. Slowly I stood up, slid my pants down and pulled my boxers off. As I stood there I grew harder by the second, and she could tell. She moved forwards some, her top still off, and started to grip my now erect cock. I was stunned. My own sister was actually touching it! Slowly she started stroking it a little. I was in heaven! I closed my eyes and let my sister work. Occasionally she'd stop, adjust herself, then feel it again. After a few minutes I looked down.
'I'm going to shoot sis...'
She then stopped stroking and took her hands away.
Knowing I was going to shoot any second I started jacking on my own, shooting several loads onto my sisters chest and shoulder. My sister almost sat there in horror seeing my cum shoot out, string after string.
'Eww, you jerk!'
She stood up, picked up her shirt and bra and went to the bathroom to clean up. I just grabbed my boxers and cleaned off my cock as to not drip on the carpet. Feeling a little more audacious I went to the bathroom after her, my cock still hanging out. I stepped inside to find her standing in the mirror with her top still off, using a towel to wipe off my cum.
'Sorry sis, I didn't mean to do it like that.'
'Just don't tell anyone what happened, ok?'
'Oh yeah, of course.'
She then gave me this sort of disgusting look, indicating that I should leave. I did, going back to my room to dress again. That was the end of our relations that day, and we never talked about it again. I still think about that day though and the short, yet fun, time my sister and I had together.