Ty felt Eileen wish for something, and a strange shiver ran through him. He could tell it hadn't affected Eileen, and he said in their head, "Uh, Eileen, what did you just wish for?"
"Well, since you just used this body to introduce me to the male sex," Eileen explained, "I thought I'd return the favour. So I turned your sperm self from having a Y chromosome to an X."
A whole load of intense sensations were swirling through Ty's part of their shared mind. Eileen casually took control of their body, enjoying how it felt to return to the sex she was familiar with.
"So obviously, first off our body is gonna be much curvier and smoother," Eileen purred, and Ty felt it seem to shift around in all kinds of weirdly enticing directions. Their face turned prettier, their hips were getting wider, their shoulders and torso narrower, their skin looked almost hairless.
"Girls don't have as much muscle as boys," Eileen noted as their arm and leg muscles shrank and their hands and feet turned more petite, "but I think it makes us more elegant." Ty felt like he agreed.
"Oh, the big part is coming!" An indescribable twinge of pleasure shot through Ty and he could tell Eileen was enjoying this part a lot too. "Obviously since we're not a boy anymore, we're growing..." Ty's mind went blank for a moment at the sensation of their nipples growing intensely sensitive and warm, soft flesh. "Mmmh, I missed having my girls!" Eileen giggled, enjoying how Ty's mind was blown from growing breasts.
They peered down to their body's crotch, the sensations racing through it feeling most intense of all there. "Ok Ty, get ready for this," Eileen advised. Ty felt as ready as he'd ever be, focusing on Eileen's voice this time so as not to just get frazzled by the changes.
It felt hard not to as his manhood began to shrink. "So, you're kinda forming three things at once," Eileen explained. "Your penis is shrinking down into a clitoris that's super sensitive to make you get prepared for sex. Your testicles are forming into ovaries that carry eggs instead of sperm. And your scrotum is turning into your vagina, so it'll open up and be able to take stuff inside it."
As she described it all, Ty felt each bit take place. His cock seemed to bundle up tighter and tighter, not able to be inside anything but way more sensitive. His balls tugged up and reshaped until they linked with other parts inside him that formed a womb. And his sack shrank inwards until at last it split open, a passage forming that led inside... her.