Ty had always thought it was kinda weird how big the divide between men and women was in society, and how something as arbitrary as whether someone was born with one kind of genitalia or another made such a massive difference in how they were treated. Plus, since he'd started puberty, a part of his mind had been curious about what being a girl felt like, both in terms of social life and in terms of... that.
So one idea from his wish stood out to him: making everyone change to the opposite gender. To his surprise, thinking about it was kinda getting him hard. He decided if that's what he was gonna pick, he wanted to get the most full experience of it, so he locked his door, got in front of the full-body mirror in his bedroom, and stripped naked, smirking at his erection brought on by focusing on this weird fantasy.
He wished, and a moment later, the world froze, and 7.6 billion humans suddenly started to change. Ty felt weird feelings wrack his body as it rapidly produced feminizing hormones. His facial structure subtly altered, his hair lengthened to halfway down his back, and his muscles slimmed and turned more lithe. His balls were sucked up inside him, and he felt his body ache to be filled up, the sense that his penis was a natural part of him seeming to diminish.
His butt swelled and his hips widened, his skin seeming softer. He giggled in a higher-pitched voice as he looked at himself, and then panted as his nipples perked up. Suddenly they were way bigger and more sensitive, and Ty couldn't hold himself back from rubbing and pinching them. Pretty soon the flesh around his nipples had swelled too, and Ty was palming soft, C-cup boobs.
Before long, his penis was receding into his body, losing its definition and girth as well as its length. The place under it where his scrotum had been had flattened to a small mound, and his former nutsack was forming her new pussy lips. Once she felt her body finally open, she pushed her fingers inside and gasped at the satisfaction the feeling of fullness gave her. Her body responded to the feeling by swallowing what was left of his penis, the head receding to a sensitive clit.
With a lot of difficulty, Ty managed to withdraw her fingers from her slit and stared, panting, at her new body. She smiled at how pretty she felt she looked; it was ironic because, even though she pretty much just looked like the same person but if he was a girl, she felt so much more at ease with her own appearance.
She wasn't sure whether to get herself off, or go find out the impact her wish had had on the world...