Mark finally settled on 2x taller, a pretty basic choice but it was big enough to be obvious without being unreasonable to accommodate. "Twice as tall, should be alright, Brenda twice her height" He concentrated, closing his eyes to try and focus but occasionally peeping one open to see if worked. For a moment he started to doubt that he really could grow things, it couldn't be possible, of course it wasn't real, he probably just imagined the bottle growing earlier.
But then, as he opened one eye, he saw Brenda and she seemed to be a little taller. Then he opened both eyes and noticed that Brenda was definitely taller, taller than him now and still growing. Brenda stretched up and up, taller and taller. Her clothes seemed to shift and adjust to her body, but not completely as they seemed to be getting more and more revealing as she got taller and taller until it finally stopped. Where his meek and petite sister had once stood, was now replaced by a ginormous amazon of a woman.
He hadn't even realized his mouth was wide open, eyes wide in shock. But he shook his head and regained his bearings as Brenda turned back around. "...H-hey, Brenda?" He said meekly, his younger sister blinked and tilted her head as she looked down at him.
"How uh...how tall are you again?"
She smiled, a soft chuckle escaping her lips. "10'2". You'd think that you would remember, I am the tallest person in the world after all." A slight tease. It made sense this increased size would start to betray her somewhat old personality. Her clothes as well, the old Brenda would never wear something so revealing.
"No, yeah, of course, I was just asking 'cause, I thought, uh, maybe you've grown recently," Mark replied quickly.
After that Mark started to remember, a flurry of new memories of this new, massive Brenda. Brenda hadn't always been tall, she was about average in elementary school, nothing out of the ordinary. When she hit puberty in middle school she started growing rapidly. Doctors diagnosed her with a unique form of gigantism that was even more potent than normal but without any side effects. She was by far the tallest woman in history, so big that the family lived in a house specifically designed with her size in mind.
As Mark remembered the past, he knew that he wanted to test out his power even more. He decided to ...