Jack figured a logical starting point would be to do one simple, if big, change first. For as long as he could remember, and especially since he'd hit puberty, girls seemed totally different to him. It was particularly odd to him how even though everything from their bodies to their treatment in society to the terms used to describe men and women, deep down all that really set male and female humans apart was one chromosome. He'd idly wondered many times what it'd be like if he had a second X chromosome instead of a Y.
But this time, as he wondered the magic of the room disapperated his clothes, and he turned to look at his body in a mirror as he felt it start to change. An indescribable force shot back through his life and adjusted the sperm that had created the xygote which one day became Jack Folders from having a Y chromosome to an X, and this shift began to reverberate through time and coalesce around Jack's form in this room.
In Jack's reflection and in his body, what was male was now becoming female. His facial features changed first, his facial hair vanishing and his jawline seeming smoother. He felt a twinge in his throat and noticed his voice rise from a masculine baritone to a feminine soprano. His shoulders shifted inwards and his arms and hands shrank, and the transformation spread down his torso, which contracted to form feminine curves while his hips and thighs flared. He also seemed to turn slightly shorter, and his legs and feet seemed smaller like his hands and arms had become.
His body had not changed in one very noticeable respect, though- his genitals. But soon his nipples perked up and his penis became erect, and the last vestiges of 'he' gave way to 'she'. His phallus shrank inside him, and any negative feelings about his emasculation were overshadowed by how good it felt as the nerve endings concentrated more and more tightly together in the nub that was taking his penis's place. Her chest sprouted rapidly, swelling from A cups to B cups to C cups within seconds and feeling amazingly warm and sensitive. His testicles pushed up inside him and rearranged into ovaries, his scrotum sucking up until it barely protruded from between her legs and separating into labial lips, connecting with the vagina that had formed inside her as his penis had shrunk and her clitoris, the little nub that had formed from his penis.
Jack Folders, or Jacky Folders as she was now, looked at her new self in amazement. She looked just like he had, but totally different- she was the same person, just a girl instead of a boy. There wasn't even a hint she had ever been a boy, it was truly surreal. She stared at her body, her perky breasts and smooth skin, and wondered what she'd do with herself now...