As he stared at the handsome man before him, Ty realised a certain idea appealed to him a lot right now. Eileen seemed to have really liked turning from a woman to a man, and he felt curious about how exactly it felt- or rather, how the opposite felt. If Eileen could be a man, he could be a woman, and he decided to focus on the idea.
Instantly an intense sensation swept through Ty as his body started producing feminine hormones en masse. He exhaled deeply, and Eileen looked up at him in surprise. "Ty, are you OK?" he asked a little concernedly.
"Yeah, I just made a wish," Ty explained, a shiver racing through him right after he finished his sentence. "It's kinda like what you did, but... mmmh... in the opposite direction." His voice slightly increased in pitch after the moan.
"Wait, do you mean..." Eileen cottoned on and watched the boy's body change, just as transfixed as he'd been when she transformed.
Her amazement at seeing the change was nothing compared to Ty's amazement at feeling it. His whole body seemed to be shifting around, and seemed to be growing more sensitive. His muscles and body mass declined to make him more lithe and petite all over, and his figure changed from straight to curved. He could tell his arms and legs and hands and feet used to be larger, but they felt weirdly right this way. His neck slimmed and the larynx's bulge vanished from it, while his face and jawline softened. Even the texture of his skin felt smoother, and its hair had vanished.
Now came the most substantial changes of Ty turning from a boy to a girl, and they made themselves known through arousal and sensitivity spiking in his chest and crotch. His nipples swelled and puffed out as mammaries formed under them, and pleasured whimpers escaped his mouth as he sprouted mounds of flesh on his chest that felt soft and ached to be touched. He realised Eileen was staring at them, his cock large and erect, and felt a mix of shame and a wish to cover herself and pride at knowing Eileen loved his girlish body.
At last the only masculine part of him left transformed. He saw his penis shrink away, and realised it felt more pleasurable for it to be more small as it gradually transformed into her clitoris. While it shrank, his balls pulled up inside him, and reshaped into ovaries, and his scrotum receded into his crotch until the seam that ran across its middle opened out into a vagina.
Once the changes finished, Ty's mind instantly adopted- she was a girl now. And as she looked over at Eileen to see his transfixed face and rock hard cock, she realised she wanted to fuck him so bad.