Warning: this story is a fantasy and details sexual behaviour that is, at best ill-advised. But it is pretend, so so long as you aren't a doofus, you should be ok. All sex-acts described are within ages of consent in the country it's written in (England, for the record).
This is also an introduction, and the next part is already conceived and can be out soon if I get some positive comments that anyone wants to read it!
For the third time in the last five minutes, Penny silently scolded herself and tried to focus on the movie on TV. Ok, so they were actually only step-sisters but she'd known Natalie since she was five, and the way she'd been looking at her across the sofa was all wrong. Apart from anything else, Penny had never looked at any girl that way β she may've been single at the moment, but she'd had a reasonable share of men at uni, and they'd had a reasonable share of her. But Natalie was fascinating her...
As she tried to ignore her desire to look, Penny's mind puzzled at why she was looking at a girl she considered a sister in such a weird way. Maybe it was how different they now were. When they met thanks to Natalie's dad and Penny's mum, they were five and nine, and both kids. Besides, Penny's actual sister was there too, and they formed a close family unit and were all basically kids. Sure, as they grew the fact that Penny and Hannah (her elder sister) were slim with glossy, black hair and pale skin, whilst Natalie was a more tubby kid with tumbles of deep, auburn hair, made it clear that they were not blood relatives, but they behaved as if they were. Now however, at 19, Natalie had very much grown into her body. Penny (23) and Hannah (25) were almost exact replicas of each other, and were often mistaken as twins at a glance. Penny had C-cup breasts to her sister's Ds, but also had an eye-catchingly spankable bottom compared to Hannah's more slender butt, but they were both a slim size eight and shared clothes between themselves. Natalie, though a similar height and still with a slim frame, was altogether more voluptuous. Though her waist was slim and toned, her hips flared out to a full, curvy bottom necessitating size 12 jeans, and despite her slender back, she'd grown big, soft, F-cup boobs. And it was at these, or more specifically the deep cleavage formed by the way she was splayed on the sofa, that Penny found herself staring.
Dragging her eyes once more from her sister's breasts, and trying to put the strange thoughts out of her head (What would Natalie look like naked? What did she like in bed?), Penny downed the remainder of her glass of white wine and poured both girls another, smiling at Hannah as she walked in from the kitchen. Both Natalie and Penny were staying with Hannah over the Easter holiday. All were single, as it happened, and were enjoying spending time together, shopping, drinking and spending time together. Resolute now, Penny gave all her attention to the movie and clamped down on her odd thoughts β she needed to forget all about this as she'd be sharing Hannah's spare bed with Natalie in an hour or two!