Ty decided what he'd really like to try first was changing sex. He'd always wondered what it was like to be a girl, and had found it so weird how differently girls acted and were treated compared to boys. It felt like a secret he never got let in on, and since he learned in biology how you have a nearly even chance of being born male or female, he'd wondered what life would be like if the figurative coin toss had landed the opposite way.
Getting up, undressing and standing in front of his bedroom mirror naked, Ty wished, "I wish I was a female version of myself." In his mind's eye, he saw his conception, and the coin toss of his body's creation became reversed- the Y chromosome he had had turned to a second X.
Like a chain reaction, the shift rippled through to catch up with him, and he watched as his current form transformed from male to female. His figure shifted, his shoulders shifting inwards and his hips widening outwards, muscles turning from firm to lithe, his arms and legs and hands and feet shrinking subtly.
His skin seemed to soften, and turned smooth as almost all its hair thinned except on his head, where it lengthened outwards. Even his facial features changed, his cheeks turning softer, his lips puffier and his jawline less pronounced, his larynx vanishing into his neck as his masculine baritone faded.
The most obvious change that a second X chromosome caused started to make itself known at last. He felt an odd sensitiveness in his chest, and saw his nipples perk up and swell beyond their natural size. Instinctive fantasies akin to the ones he'd had since he started puberty, but strikingly different, were forming in his mind. He imagined having someone rub his nipples, pinch them, suck them. His hands moved to them, and he panted and whimpered at how pleasurable it felt. In response to the indulgence in his feminizing body, mounds of flesh started to form under them, and Ty's eyes widened in a mix of surprise and pleasure as he formed breasts.
Only one part of Ty's body had not transformed, and he looked down at it and felt an even stronger instinctive fantasy come over him. Ty felt the urge to be impregnated. She could have a body that could bear life if he gave up his masculinity. Without hesitation, he accepted this, and his penis started to shrink away, growing more and more sensitive as its size diminished. His testicles moved up inside him and were rearranged, the sperm binding into an ova while they shaped into ovaries. His scrotum tucked inwards and the seal down its middle parted as it connected with a new passage forming inside her. A vagina connected to a womb.
As the changes finished, Ty felt something click- she wasn't a boy anymore, she was a girl now. She looked at herself in the mirror and saw the same person she had seen before her wish, but someone who was the opposite sex. Even her instincts had reversed- while before he had felt instinctively attracted to girls, now she felt instinctively attracted to boys.
She wondered what to do with her transformed body...