After you've both recovered, you pull out of her, and suddenly feel kinda weird. "Are you OK?" she asks, neither of you even noticing that she just said that in Japanese.
"Yeah, I think," you reply, also speaking Japanese as fluently as you knew English before. "I just feel kinda weird."
She winces, and replies, "Yeah, same here actually." The two of you watch and feel your bodies start to change.
Her jawline seems to turn firmer, a bulge forms in her throat and her voice seems to deepen. At the same time, you notice your voice rise a few octaves as your skin starts to turn softer and smoother.
Both your muscles twitch, and you see her arms and hands grow larger while yours slightly shrink, her shoulders suddenly seeming slightly wider while you could swear yours have narrowed.
She grunts as her chest seems to shrink, her boobs flattening into a toned, slim chest, and your own body starts to sprout breasts, your nipples perking up and widening as soft mounds of flesh form around them.
As the changes move to your lower body, and your girlfriend's hips and butt shrink and turn firmer while you develop a curvaceous figure, they start to take root mentally too. Your old sense of self is rapidly overwritten by this new body, with the surge of hormones asserting it to you- you are female now. Likewise, your girlfriend is rapidly embracing his newfound masculinity.
Soon after, the last vestiges of your old sexes are replaced. His pussy seals up and large balls form inside the new scrotum, and his clit rapidly swells and grows several inches until a thick shaft hangs from him. As he finishes changing into a man, your own cock shrinks down and rapidly grows more sensitive while your balls are tugged inside your body, and the sac where they hung tugs up and opens out into a slit leading inside you.
Once you've both finished changing, you look at each other in amazement. It's so weird to realize he's become a boy and you've become a girl, and you're both indescribably eager to find out how fucking would feel in your new forms.
"Babe?" he says in his new, deeper baritone.
"Yeah?" you reply in a softer, higher-pitched voice than before.
"Oh wow... babe, please can I fuck you?" he continues, his hand grasping his newly-formed cock.
"You'd better," you smirk, instinctively lying back and spreading your legs so he can see your new pussy.
He quickly gets atop you, positioning his cock head against your lips and slowly pushing it inside. He groans and you gasp at how tight you feel and how big he is. Your discomfort at having a cock inside you starts to fade in favour of pleasure as he starts playing with your tits, surprising you with how rough his hands feel against your soft skin and how sensitive your nipples are.
As your pussy relaxes around him, he starts thrusting in and out of you, his head rubbing against the G-spot inside you and his balls slapping your body as he rails you. Pretty soon you start clenching round him not out of discomfort, but to try and pleasure his cock more, and he moans appreciatively as he continues to fuck you.
It doesn't take long for him to get to his peak, and he groans as his thrusts grow fast and spasmodic, and you feel his virile cock twitch inside you. When you feel the first of his cum enter your nubile body, you go right over the edge with him, and you both kiss passionately as you hit your peaks.
Once you finish cumming, you...