As their form started to develop genitalia, Ty's consciousness seemed to flash forward to his age before he'd made these wishes. It made sense- their genitalia was without function until around that age, so he could get a proper idea of what it'd be like. The development was quickly causing him to feel the same primal arousal he'd felt when Chiako and Aoki were fucking. Their sense of identity felt blurry, though in a pleasant way- they were pliable, suggestive, prepared for the genes they had been given to take their course.
As unfamiliar feelings welled up in him, Ty realized something was... different. They had two X chromosomes in this body. The point at which a genetic signifier of the Y chromosome was to trigger their masculine development passed, and the embryo started feminine development instead. Ty felt another surge of arousal and change as this development rapidly caught up with him.
Feeling a warmth in his chest, Ty watched his nipples grow wider and longer, as well as feeling them turn far more sensitive. Once they had changed from masculine to feminine proportions, he gasped and moaned as flesh rapidly accumulated on his chest, until he had soft, firm C-cups. Feeling his figure, he realized his proportions had adjusted in other parts of his body with the changes. His arousal response had quickly adapted too- she ached to have her boobs cupped and squeezed and her nipples rubbed, pulled, pinched, sucked, bitten.
Moments later his masculine genitalia was adjusted by the new hormones. Peering over his new chest, Ty saw his penis rapidly shrink to nothing, and as the shaft and balls moved inside him, the nerve endings accumulated around the tiny point that had been the cock head, while a passage and vaginal tract formed inside as his... HER... sexual responses changed in tandem. The urge for him to fuck and fill things gave way to the need to take things inside of her. Soon his scrotum had tucked inwards and formed her labial lips, as a vagina opened at her crotch.
The last thing Ty experienced before returning to being the embryo was the overriding of her default perception. She still remembered being Ty, an American boy, but the memories of Tae, the Japanese girl she was becoming, had quickly started to fall into place. Once she was born, she'd adapt to that life as naturally as if she'd never had any other.
And looking at her body, Tae had to admit, she felt pretty happy with that.