Damon decided he'd like to start by changing genders. He and Monica had both been questioning their sexualities for a while, though they knew they loved each other, and he had had fantasies for a long time about what it'd be like if he was a girl. This was the perfect opportunity to find out.
He pressed the 'Gender Change' button and a laser came out of the machine. It slowly moved down Damon's body, and he realised as it reached his neck that it was causing his clothes to vanish. "The first step of the process is to remove your male clothing. This is stored on your receipt so if you choose to turn back later, you can restore it," the machine explained, as the red light flashed down Damon from his head to his toes, leaving him naked as the day he was born.
"Next, your hormonal balance is inverted. You may feel strange, because the concentrations of testosterone and estrogen in your body have been reversed and your Y chromosome has been converted to an X." Saying Damon felt strange was an understatement- the sensations racing through his body were indescribable. A tension overrode him, his heart was racing, every part of him seemed to be sifting around or tensing up.
While Damon was only in this state for a few seconds, it seemed to last an agonizing eternity, until at last it seemed to start to release itself. "Now your current form's neurology has been backed up, your changes are manifesting physically and mentally. Once this step finishes, you will be a female version of yourself and everyone, including you, will think of you as such." And manifest they did.
The machine's walls turned to illuminated mirrors, and Damon saw his body transform dramatically. He slightly shrank and his figure shifted to be more curvaceous. His arm and leg muscles turned more lithe and his hands and feet shrank. He saw his face shift around to look more feminine, and his skin smoothed out, much of his body hair thinning out or vanishing. A warmth in his chest and crotch accompanied the last changes, and with it came the big shifts in his self-perception. His nipples swelled up and his chest swelled even larger, and odd fantasies emerged in his head, wanting to have them played with and sucked on. He? That seemed a strange term now, those were her breasts. Dan... Damon's eyes drifted further down and he saw his crotch feminize. The penis shortened rapidly as it turned into a clitoris, while his testicles pulled up into the body and the bulge of the scrotum shrank inwards. Dana's mind accepted her new identity as her womb, ovaries, clitoris and vagina formed.
Finally, the machine ran another laser up Dana. "To finish up, we're assigning you some new clothes to suit your new body. Hopefully you'll like them!" Dana had to admit as the laser swept up her, she did kinda like what she saw- some cute black flats, white knee socks, a black skirt and a cute white strappy top with a character from an anime she knew she and her friend loved.
"Do you wish to try another transformation?" the machine asked. Dana clicked No, grabbed the receipt for her old self and climbed out. Slowly she realised something had changed about her and her partner...