Here's a little secret about Ty he'd never told anyone: he was a radical feminist. Given how shittily other guys had treated him, compared with girls generally seeming more nice, Ty had felt isolated from his gender for a few years now. He'd started reading about feminism, and the idea of a world without boys and men sounded amazing. Artificial insemination technology meant you could actually have a society comprised only of women, so maybe a society based on women and female values might actually work?
Of course, even if someone tried it Ty could never be a part of it- after all, he had figuratively failed step 1 by being born a boy, and no matter how badly he wished to be a girl, he knew they'd never accept him even though that's who he was deep down. He'd hoped maybe he could donate his semen so they could use the X chromosomal ones to reproduce, but even that was probably a lost cause.
But now he had his power, he could create this utopia. He smiled as he thought of it- not just some societies, but the whole world could be female, forever free of patriarchy and sexism. And it didn't need to just comprise a relatively small number of women who were bold enough to accept this new future- he could proselytize it and free all boys and men from their gender difference. But naturally, the first person to be liberated from the male sex would be Ty himself.
Undressing and getting in front of his bedroom mirror, eager to see his deepest desire realized, soon Ty was stood naked in his room, his anticipation brewing as he looked over his male body for what he knew would be the last time. Silently he wished to have been born a girl instead of a boy.
Ty exhaled with a sense of relief, and felt his body start to tingle all over. The wish had shot back through Ty's life to before the xygote that would form him had been fertilized, and it changed the Y chromosome of his sperm to an X- the ripple effect of this change was racing through his body, making it become her body. Ty watched as his skin smoothed out all over, his body hair thinned or vanished everywhere except his head, where it lengthened rapidly; his facial features softened, his lips grew puffier, his firm jawline rounded out and his larynx no longer protruded in his throat as his voice increased in pitch.
His figure followed suit, his shoulders shifting inwards and his torso curving slightly as his arms and legs turned more lithe and shapely and his hands and feet seemed more small. Ty felt a twinge of pride at the newfound elegance of his body, renouncing the feeling he'd had as a boy that he had to be strong and handsome.
As the wish moved at last to his genitalia, Ty smiled at the thought that some men believed that a phallus gave people some weird superiority to the point that women envied it. Ty instead envied the vagina, knowing it gave more pleasure in sex and the capacity to bear young, and the breasts, a conduit of pleasure and a source of milk for offspring, and the knowledge that very soon he would have them instead of a penis was the most exciting feeling he'd ever felt.
Ty's nipples perked up and his penis turned hard for the last time. Within moments, he moaned in a high-pitched tone as he ejaculated hard, somehow knowing that the semen he had shot from his penis only had X chromosomes. Once his orgasm subsided, he felt his balls tuck up inside him, his scrotum tucking inwards as it started to adjust from a sac into lips. As his balls moved into his body they rapidly reshaped, forming into ovaries as the sperm within them bound together into ova.
The large shaft between his legs receded rapidly into Ty's body, and as he watched his penis vanishing and felt vaginal lips open under it, his emasculation clicked in her head. He was becoming she, a male turning into a female, a man into a woman. The prefixes felt comforting, liberating even. How much more sensitive his rapidly shrinking penis felt as it was becoming her clitoris certainly added to that feeling.
Soon she noticed the warmth and swelling feeling in her chest, and panted and moaned as she felt soft breasts start to form around her larger, more sensitive nipples. As she sprouted, she felt the same pride she'd felt at her body's changes earlier as they grew more dramatic, large warm C-cups soon hanging from her body.
Slowly she came down from the high of her transformation, and once she was focused enough to pay attention to her new form, she gazed at herself and smiled. Not even a trace of her former masculinity still showed, and she loved how she looked.