The option that jumps out to you is 'Gender transformation'. You aren't sure if this thing is somehow tracking your history or it's just a more common kink than you thought, but you're thrown because that's one of your biggest kinks. Hell, most of the time when you're on CYOC you like to read gender TF chapters. You've even written a few. But you've always felt kinda sad about it because you know it's impossible. Or at least, you thought you knew.
You click the option, highlight yourself, switch it from 'Male' to 'Female' and, just before clicking 'Apply Change', you decide not to take any precautions. You lock your door and undress, throwing off the T-shirt you were wearing, your pants and your boxes. The Chronivac scans your naked form again and once it's done, you take a deep breath, and with shaky hands click the 'Change' button.
A bright pink light washes over you and then fades. For a second, you don't feel any different. And then... shit... an intense tingling builds up in your head and spreads through your body from the top down. Masculine hormones are getting displaced in favour of feminine ones.
You get a look at yourself in the mirror and see how your features are starting to alter all over. Your hair has lengthened rapidly. Your face seems the same until you feel a shiver pass through it, squint your eyes shut and see it's subtly reshaped into its feminine counterpart.
It spreads further down, making your shoulders slink inwards, your arms and hands get more petite, your torso slinks inwards and your skin smooths out, getting hairless and supple. The feminizing hormones cascade down you, spurning your hips to widen, your butt to fill out and your legs and feet to turn lither.
Just two parts of you have not turned completely female because of the Chronivac, your chest and your crotch. You hear yourself breathing heavily as femininity emerges in the first of these. Within your chest mammary glands form, and with them forms a second erogenous zone. Your nipples swell and get sensitive, and soft, warm mounds of flesh expand around them, your pleasure intensifying as you softly cup your forming breasts.
Your tits continue to swell until they reach a C or maybe D cup, and then stop. You reluctantly let go of them when you feel the feminine hormones reaching their opposite and starting to seize and reshape it. Before your eyes your penis starts receding. Your phallus seems to grow more and more reactive as it shrinks away. A womb forms inside you and it reaches inside your scrotum to your testicles- tugging them up inside.
It's at this point that you feel your connection to masculinity fade. You just got castrated by the Chronivac, and it felt good somehow! The male you were is continuing to vanish- your scrotum turns flush with your crotch and splits open into a vagina. Your tiny cock continues to shrink until it settled into place as a sensitive nub above your slit, giving you a clitoris.
You stare at your new self's reflection for a moment after you finish changing. You really have changed from male to female- and not in a fictional chapter of some story on a website, you're actually a woman! It... it feels so nice. You lightly hug yourself, thrown by how this body feels, and wonder what to do next...