Ty decided that, at least at first, they'd have nature take its course. Apart from anything else, if they weren't happy with the person they became, they could just wish to be different.
When Chiako's semen started to reach their body, they realized they were more than happy with that choice. Constantly being rubbed along by the tiny cells felt like someone touching his body at an orgy. Every time they felt a sperm tried to burrow inside them, they saw in their mind's eye the person they'd become. They barely saw one they weren't happy with, and eventually, after a few minutes of seed chewing through their walls, one finally came through and fertilized them.
Rapidly, they turned from two cells combined into a mass of cells which became a xygote, and in Ty's mind's eye something weird started to happen. He still remembered being his old self, but his sort of default perception of what he looked like had started to shift. He didn't see a white boy now but an Asian one, and one who clearly came from Chiako and Aoki's DNA. Technically, they were his parents now, though he still felt detached from them in that respect.
Guided by biologically instinctive motions, the xygote that was Ty lodged itself in the wall of Aoki's womb and impregnated her. Having done so, Ty slowly started to grow, and rapidly formed basic human characteristics. Within a few minutes for him, 6 weeks had passed, so their genitalia was about to form. Now Ty would find the sperm that had fertilized them had had...