She didn’t grow much, not on that first day.  It was enough that Kyle noticed, and commented while preparing her breakfast.  “I’ve grew a whole inch overnight,” she replied happily.  “Some of that can probably be accounted for by time of day variance – you’re taller in the morning than at night, you know?”

“That’s probably all it is,” Kyle reasoned, setting a small plate of eggs in front of his sister.  “I don’t care how effective this treatment is – people don’t grow THAT fast.  At least, not for long.”

Monica said nothing, though her smile spoke volumes.

By the end of the week, there was no longer any doubt.  Monica was growing at a pace that could hardly be believed.  Now four feet five inches tall, she had been required to raid a trunk full of Kyle’s old childhood clothing just to find something that fit.  He teased her about this, but had to admit she looked good in his old Ben 10 t-shirt. 

In addition to growing taller, Monica was filling out rapidly.  The only ways it had once been possible to tell her from a normal nine year-old girl had been by the maturity of her eyes, and the intelligence with which she spoke.  Puberty had come for her at last, and had apparently arrived with every intention of making up for lost time.  Her breasts, still quite small but very firm, were getting bigger every day.  Her hips were wider than the previous week, her ass much rounded and curvier.  Her short blond hair was growing much longer and thicker as well.  She even, much to everyone’s surprise, seemed to be getting more athletic.  When Kyle noticed the faint development of muscle on her forearms, he promptly challenged her to an arm wrestling match.  Monica politely declined.

With her new size, Kyle found himself willing to listen when Monica argued that they could do more than sit around and watch television all day.  He could find her easier in a crowd, she reasoned, and even if she was still extremely petite, she at least wasn’t as fragile as before. 

Truth be told Kyle was happy to find an excuse to lift Monica’s virtual house arrest.  It would have been tragic to pass an entire summer without ever leaving the house.  That, and there was something about her new appearance that made her arguments far more compelling.  She was visibly a woman now – albeit one whose head came no higher than the middle of his chest – and so it was impossibly to dismiss her requests as simple childish desires.

The two began going out almost every night – to movies, or local concerts, or sometimes just out to dinner with the money their parents had left.  Their little sibling dates were wonderful, except for one little problem: when they were away from the house, Monica was always incredibly clingy.  She would self-consciously slip her tiny hand into his from across the table at dinner, or lean her head against his arm as the lights came down in the theater. 

Kyle fought himself over these gestures of affection, and in the end decided Monica was just nervous to be out among so many people at her new size.  She was looking for comfort, that was all.  He was glad to provide it, but it awakened certain feelings in him that were decidedly awkward.  Kyle had been single for many months now, and the way Monica touched him was eerily similar to the way his last girlfriend had when they were out on dates.  He resolved to ignore it, but this was becoming difficult.  Day by day Monica grew taller, developing into an extremely attractive young woman.  He began to notice more than a few jealous looks from other men, who were unaware he was just out with his sister.

Ten days after Monica’s treatment, Kyle awoke in the middle of the night, a half-remembered and very vivid dream still fresh in his mind.  He stared about the darkened room, catching his breath, trying to recall the details.  It had been something pleasant, and from the scraps that he could recall, highly erotic.  There had been a woman, with eyes hard and dark like obsidian, yet those eyes were very kind.  He could remember the heat of her as she pressed against him.  And her scent…alluring and naughty, all sweat and musk and a faint twinge of something floral.  She touched him…he had felt that, almost unnaturally real.  He had wanted her to touch him more.  But then, something had made him wake.

Kyle settled back under the covers, determined to try and recapture the dream.  He’d just started to drift off when a strange sound came from the other room.  A voice.  Possibly one in distress.  Reluctantly he went to investigate, padding as quietly as he could down the dark hall in his bare feet. 

The sounds were coming from Monica’s room.  It was her soft voice, murmuring, sometimes groaning.  They weren’t noises of distress.  His dream came flooding back, and in an instant he knew what those sounds were.  Kyle made up his mind to leave his sister in peace, but something almost like a compulsion made him stay.  The door was open a crack, and silently, Kyle nudged it wider.

The smell was the first thing he noticed – it was the exact one from his dream.  He realized suddenly he’d been smelling it for days: a faint background whenever Monica was near.  Never had it been this intense.  Underneath the blankets, he could see the shape her body as she rhythmically rocked…back, and forth.  The sounds slowly grew more and more frantic, building toward a crescendo.

Kyle shut the door before she could finish.  He returned to bed, feeling guilty.  It took him a long time to fall asleep.