I've always felt a little guilty about this, but a few other guys here have posted similar experiences, so I guess maybe I'm not that bad, so here goes...
I guess I've been masturbating on and off since I was about fourteen; at that age, I ran into the world of soft-core pornography on the internet, and it took only a few weeks for me to become accustomed to myself! After a few weeks of euphoric delight at anything showing girls in a state of undress, I like to think I 'normalised' as I only really seemed to be turned on by the erotic, more genuine photos of girls my age - fake lesbians in excessive make-up did nothing for me anymore, only 'the real thing'.
I have a non-identical twin sister who's a whole hour older than me (well imagine we WERE identical - nah!). We've always been close, best friends as well as siblings. Around about the time I first got into soft porn, she started to really develop into a spectacularly hot girl - she had the perfect hourglass figure with a thin waist, gorgeous round hips, a nice tight ass, and luscious 34b breasts. As my fnatasises developed, I began to find myself viewing her in an admiring light as well as seeing her as my sister.
I was a little later in developing than her, but when I reached sixteen, she would tell me I was growing into a well-toned, lovely young man. So we'd jokingly tease each other about how 'hot' we each looked.
Around my seventeenth birthday last July, we were getting a little more teasy with each other. Then came the summer heat wave.
It was around the first week of the summer holidays when we both had our first lay in (up until then we were redecorating the house, so had erratic sleep at various friends' houses). Our mom called up to us that it was midday, and we laughed from our bedrooms as she told us she was going out for the day, and that we shouldn't wait up as she wasn't due back until the early hours. Well, me and my sister Kiera (seems I forgot to name her, lol) had a conversation via shouting from our rooms that we might as well get up now we'd been woken up.
I felt hot and sweaty almost instantly, so jumped out of bed in my naked state and decided to go cook breakfast straight away then shower; I was too hungry to wait. I was halfway through my brunch when Kiera came down; she'd obviously not bothered to dress, and was embarrassed to find me silently munching away on fried egg and toast in a similarly-naked state at the table. Well, Kiera was as hungry as me, yet I'd used up the last of the egg and the bread, whoops!
We both decided we were too lazy to go to the shop, so I suggested she share my food. I was munching away on a slice of toast when she knelt on the table in front of me and bit the toast while it was half in my mouth - a bit kinky I had to admit! She giggled and blushed as she swallowed it, then slyly grinned at me. I laughed back at her, and she sneakily stole my final slice and gobbled it in one. Naturally, I was outraged, and leapt out my chair to 'get' her. She screamed and ran into the lunge, laughing as she skipped. I bounded behind in that just-woken-up kind of way, and she dived onto the couch. I dived after her and lay on top. She beamed.
It's safe to say we were both in pretty compromising positions, so we both laughed out loud and then quickly sat up. I found myself gazing at her figure, and it looked very nice. She obviously noticed, and smiled and chuckled once more. She pushed me back so I was slumped against the armrest, then lent forward onto me. Her lips pressed into mine and her breasts pressed into my chest, and she slid a tongue into my mouth. We kissed for a few seconds before she broke it off grinning and blushing, saying 'Hey Tim, no harm in having fun together!' I couldn't help myself having a boner, which Kiera gently grasped and slowly slid her hand up and down. I was just getting into it before she said 'Follow me if you want more of that, Timmy' and galloped upstairs.
Excited, I chased after her, a little horny and a little confused, but still I followed! I found her standing in the bathroom grinning, naked and gorgeous, with a shower running. She stepped into the cubicle, and I followed behind. She slid the door, then pressed her body hard into mine and passionately tongued me. I repaid the favour, and we snogged and caressed for ten minutes. Then she guided my hand to her pussy and she clasped my penis and we masturbated together, before kissing some more. Giggling, we rinsed off then dried each other.
She held my hand and led me to her bedroom and pushed me onto her bed before climbing on top of me and cuddling me. We slept. I woke first, noticing it was 2am, and fell asleep again.