"...gender room, is that right?" Billy nodded. Lucy turned around and pulled out a key from the safe. "OK, you're in room 57. Hope you have a nice stay!" She smiled cutely as she handed Billy the key.
"Thanks," he replied. "By the way, just to check, how do we do the changes when we're in the room?"
"Same as any of the rooms at the Transformation Resort- you just have to wish for the change you want," Lucy said.
Billy and Mary headed towards the room, still kinda disbelieving that this resort was for real to a degree. They soon found room 57, unlocked it and went inside.
After setting down their bags, Mary said, "OK, are you ready babe?"
"I guess so, yeah," Billy agreed. He let her take his hand and lead him to the mirror. "Do you have a plan for this then?" he laughed.
"Yep," Mary replied. "I was thinking, how about we get naked and both wish for the change at the same time? That way we can watch each other change."
"That does sound pretty fun," Billy agreed. He kissed her, and they pulled off their clothes until they were stood next to each other, staring at their naked reflections.
"OK, so 1, 2, 3, wish!" Mary laughed. They both focused on the idea of changing gender simultaneously, and after a moment they both felt a surge of arousal and a tingling sensation spread through their bodies. Billy's body was producing an unprecedented amount of feminine hormones and Mary's an exponential amount of masculine ones, and their effects rapidly appeared.
In perfect sync and parallel to one another, their bodies started to change. Billy shrank a few inches and Mary grew taller than him; his muscles turned more lithe while hers grew larger; his hands and feet subtly shrank while hers enlarged. His figure seemed to slope inwards and curve outwards while hers took on a straighter shape, his shoulders slinking inwards while hers pushed outwards, his hips widening while hers narrowed.
They watched as their faces seemed to switch to appearing more like the genders they were becoming. Billy's cheeks and jawline softened while Mary's grew sharper, and the bulge of his larynx vanished from his neck as one appeared in hers, while his neck turned more narrow and his wider to fit the proportions of their shoulders. His lips turned softer and puffier while hers became more subtle and firm, and his skin adopted a smoother texture all over while hers roughened. His hair extended until it touched his back and hers receded to a masculine cut, and he became almost devoid of body hair while thick wisps of hair protruded across her skin.
At this point all but their genitalia were the opposite gender to that which they had been before the two of them made their wishes, and now these too started to invert. As Mary's breasts rapidly receded into her pecs and her nipples turned small and masculine, Billy's nipples expanded and grew sensitive as he formed mammaries, and soft flesh sprouted on his chest which he felt a desire to have played with.
Lastly, their reproductive systems inverted- Billy felt his penis start to recede into his body and his testicles pulled up from his scrotum inside him as they rapidly turned into ovaries, while Mary felt her clitoris swell as her vagina sealed up and her ovaries moved down and stretched it into a sac as she formed testicles and a scrotum. Billy saw her clitoris continue to expand until it was much larger than his penis, which felt much more sensitive as it shrank away, and at the exact same moment their changes finished: Mary's penis formed a seven inch erection with a throbbing head, and Billy's became a clitoral nub while his scrotum pared into a vaginal slit.
Once they had switched, something clicked in both their heads- a new sense of their identity. Billy became Billie, thinking of herself as a woman, and Mary became Mark, thinking of himself as a man. They remembered who they had been, naturally, but they felt comfortable with their new sex.
And speaking of sex, they found each other's transformed bodies deeply arousing. Billie was attracted to men and Mark to women, just as their old selves had been the reverse, and they felt no doubt or confusion over their new sexuality. They hugged each other and kissed passionately, and Mark felt a twinge of desire as Billie's soft breasts touch his chest while Billie felt a surge of anticipation as Mark's hard cock ground against her stomach.
Once they broke off their kiss, they wondered what to do first...