To your surprise, your girlfriend starts undressing. "Why are you taking your clothes off?" you ask. "The guy said they change with the room."
"Yeah, but don't you wanna see our bodies changing?" she points out. That's a good point, you realize, and you start to get your own clothes off. Soon, you're stood there looking at each other naked, slowly getting to grips with the fact that soon you won't have the same bodies.
"Do you wanna go first, or should I?" you ask.
"Well, I had an idea about that," she suggests. "How about we both change at the same time?"
"That sounds fun," you agree. Your hearts racing, you both walk to the mirror, look at your naked reflections, hold hands and shut your eyes to focus on transforming.
You open them and both watch as in perfect sync your bodies start to transform in opposite directions. Your hair cascades down your back as hers tugs inwards until a short masculine cut sits atop her head. She starts to gain muscle and height while your figure slims and forms curves, her shoulders widening while yours narrow, her arms and hands and legs and feet enlarging while yours shrink, meaning she turns taller than you. Her skin roughens while yours smooths, stubble and a sharp jawline emerging on her face as your facial features soften. Your genitalia are the last things to be reshaped- as her chest recedes until only small nipples top firm pectorals, you start to sprout and your nipples widen and grow sensitive as you grow breasts. Finally your reproductive organs' old functions are erased and they develop new ones- her vagina seals up to form a sac into which she pushes two testicles, and you become castrated as your own balls tug up inside you to connect to a vaginal tract, your scrotum peeling open at its centre into a slit. Your penis withdraws into you as her clitoris enlarges and swells until she-or perhaps he is more appropriate- has a thick phallus and you a tiny sensitive nub.
As you both look at the person you love, you realize your feelings for each other are unchanged, and experience irresistible arousal from your new sexes. His penis becomes hard, your nipples and clitoris turn erect and you start to feel female juices moisten your slit. You kiss each other lustfully and hastily move to the bed, his body ending up above you with his newformed shaft pressing against your stomach. He soon positions himself more carefully, and eases his cock inside you.
It feels indescribable. It's unlike any sexual feeling you ever felt as a boy or man, to say nothing of having his hands carefully rub and pinch at your nipples. Having someone inside your body feels so right, not in spite of the feeling of disconnection from the man you were before but if anything because of it. And the man who was your girlfriend looks so handsome like this. He starts to thrust in and out of you slowly, and your body clings to him, you moan appreciatively as he makes you feel perfect.
Pretty soon he starts to lose control of his pace, pounding you faster and faster, his hips and balls slap against you with each thrust, and you get closer and closer, until... you peak and your mind goes blank for a moment. All you can think of is that thick shaft filling you, and he groans as he reaches his own orgasm, shooting his seed deep inside you, indelibly connecting the two of you.
You kiss messily and collapse in each other's arms comfortably, his shaft still inside you. You drift off to sleep, and when you wake up...