After hitting apply, John started to feel funny. His body was tingling, but he still had it in the back of his head that this whole thing could be a joke.
The tingling increased, this was no joke, the machine was doing something. First his skin tingled, he noticed shortly afterward that every pimple on his body had disappeared.
Then came some of the things that happened to him after puberty, his chest and arm hair disappeared, his muscles followed shortly after. Though he didn't speak, he imagined his voice changed back to what it was when he was 10.
Then the real changes started. He felt a tingling between his legs and realized his manparts were being replaced by their female equivelent. He was female. There was more tingling, and her hips became wider. Her butt followed suit, and she quickly realized had she been born a girl she would have had a "bubble butt". Her stomach flattened, waist got tinier, and finally grew breasts. She realized that she was quite well endowed, while her face became rounder, lips plumper, and hair longer.
She ran into the bathroom and shut the door. "Katie! get dressed, we're going to get lunch soon," her mom shouted. Reality has changed along with her, she realized. She was now Katie.