My parents were both away for the weekend again, and although I'd told my sister Sarah I'd be out all afternoon, on the spur of the moment I invited my friend Ben back to our house for a beer after karate practice. Sarah didn't seem to be around - probably out with her girlfriend, I thought. We went to the downstairs bar, where we could hear the pump going in the spa next door, the bubble-jets and something else - it sounded like a woman moaning and crying out in pain. I stepped through into the entrance to the spa-room. There's a glass partition with an etched pattern of palm-leaves, coconuts and tropical flowers. But there are also patches of clear glass and through these I could see Sarah naked, standing waist-deep in the foaming bubbles. Her head was thrown back, her eyes closed, her mouth open. With both hands she was kneading her firm brown breasts. It was Sarah who was making the sounds, because she was standing, legs apart so that the force of the main jet was playing on her pussy. My little sister was masturbating with the jet of water.
My mouth open, I watched my eighteen-year-old sister having a series of mini-orgasms. I could see the ripe swell of her buttocks above the foam, the long graceful curve of her back, her broad slim shoulders, and her dimpled brown arms flexing as she rhythmically rubbed her breasts to increase her pleasure. Even though she was my sister, I felt my dick swelling.
'Shit, man,' whispered Ben in my ear. 'She's right into it. Let's join her.' He was already stripping off his teeshirt, shorts, underpants. His penis was coming erect too.
For the past couple of years I'd been noticing how lovely and sexy Sass had become. She was tall and slim, but since the age of 14 had filled out in womanly curves -- small firm breasts, a swaying rounded ass above long well-muscled legs - while her face had lengthened, her cheekbones broadened, her mouth had become full and ripe. She was full of mischief and spirit -- hence her family nickname -- but also seemed increasingly to be aware of her own body and its effect on men -- and its effect on me. Once or twice she'd surprised me looking thoughtfully at her legs or breasts, and hadn't seemed to mind. She'd always been cuddly and affectionate, and many times in the past few years I'd found myself becoming hard when she was hugging me, her head nestled on my shoulder and her long firm body against mine, the warm smell of her skin and hair in my nostrils. She must have noticed my arousal, but hadn't drawn away. Neither of us had said anything about any of this.
I'd had dreams where Sarah and I were kissing, tumbling into bed together naked, and in the dream this seemed maybe a little bit wrong, but also perfectly natural, although I'd wake up feeling guilty and ashamed. I'd read in one of our first year psychology textbook that we learn about sexual attraction from our own families, and we're often attracted to people of the same physical type as our parents or siblings. Certainly Sarah with her lithe brown figure and long black hair was my ideal of womanly beauty.
Now, confronted by the sight of my gorgeous sister in sexual ecstasy, and with Ben leading the way, I let go of my doubts and hesitations. My body took over from my mind, and I slipped out of my teeshirt, jeans and briefs, so that my dick bobbed free. We padded in, feeling the warm, moist air of the spa-room on our skin, our stiffening penises swaying in unison. The room felt full of possibility.
