"I wish for the next seven days me and karyn swap body builds including muscle and bone structure".
Jon felt his body shifting, bones in his body were moving slightly and changing his shape, his arms and and hands got smaller and daintier, but his pants had gotten tighter, his hips and thighs had gotten wider, and his feet had shrunk noticeably, his shoulders and chest got thinner. looking in the mirror across the room, his face almost looked like a girl's, it was still him, just incredibly feminine and rounder.
Karyn was going through mostly the opposite changes, she felt like she was getting bigger, her arms and hands got bigger and rougher, her shorts felt loose as she lost her hips and her thighs, her chest and shoulders got broader, and she had to take off her shoes because they were too small, she looked at the mirror to see her own face, but it wasn't exactly the same, she couldn't exactly pick out what had changed but it definitely looked more boyish
both of them looked in stunned silence at themselves and at each other for about a minute before one of them spoke