Derek squirms in his sisters arms, desperately trying to escape. His legs kick wildly in the air as he finds himself further and further away from the floor. Looking up he sees his younger sister, growing stronger and taller with each passing second. She's almost touching the ceiling! Desperate, Derek calls out to her, hoping to save himself.
"Melissa, please don't do this, come on, it's me, your brother. You wouldn't kill your brother?"
Derek feels the shrinking stopping, and lets out a sigh of relief, believing the nightmare to be over. The relief is quickly swept away from him as Melissa grabs his now action-figure sized body with one hand and lifts him up to her face. A wild grin adorns her visage, a grin that makes it clear to Derek that she is not finished.
"You should've been nicer to me when you still could. As far as I'm concerned, I have no brother. Just a muscle-bound shithead who has the same parents"
And with one smooth motion, she swung her arm against her chest, pushing the shit-head deep between her cleavage. He barely had time to scream before he sunk deep within her, and at last, Derek ceased to exist.
Melissa smugly watched the last of the tiny man disappear. The source of a lot of her pain was finally gone. Her elation didn't last long, however, as she was suddenly overtaken by a massive headache. The headache only lasted for a few seconds, but it felt as if her head was being struck with the force of a thousand suns. Once it was over, she quickly realised what happened. She had absorbed Derek's intelligence, she was way smarter now!
She looked down at herself, surveying the gains. What had once been the body of a teenage girl who didn't exercise enough was now the body of a star athlete. On top of that, she'd gained his height, and when added to her old height, it left her standing at a towering 11'6''. At last, but certainly not least, in between her legs sat  a rather large di-
"EW!" She screamed, her eyes finally noticing the rod dangling between her legs. "Nonononono, I don't want his dick, go away please" She begged, shutting her eyes so she didn't have to see it anymore. She felt an odd tingling sensation between her legs, like something was being sucked up inside her, and felt herself grow slightly bigger. Opening her eyes, she saw that the rod was now (thankfully) gone, in it's place a familiar pussy, although it seems far bigger now. Speaking of bigger, she is now absolutely massive.
"Hmm" She thinks, "I should probably do something about my size. I can't really walk around the house like this, and I'm not ready to reveal what I can do to the world. Damnit, if only I could shrink smaller"
As if it was listening to her, her body started to shrink suddenly. It was so sudden she lost her balance, falling on her ass. "Owww....." She whined, standing up while rubbing her sore rump. She quickly realised what happened. "Holy shit, this is awesome,". She retained most of the musculature and was a little taller than she had been when she woke up, however she was not a giantess anymore. Her tits were a little smaller, a fact which she lamented, when, almost on command, they blew up once more, expanding to KK-cups. At first she was shocked, but that shock quickly turned to pleasure, then groping, than violent groping. Melissa let out several moans involuntarily, before deciding to stop herself, knowing there would be time for masturbation later. She shrinks them back down to more manageable DD's, and begins to plan what to do next...