With how exhilarating the transformation had been, neither of them wanted to hold off from their new bodies' desires any longer. "Babe, I wanna fuck you," Mark breathed in his deep baritone.
"Good, cause I want you to fuck me," Billie replied in her higher, womanly voice. Her heart raced as she felt him carefully pick her up, and she wrapped her arms and legs around him, kissing him passionately as he carried her to the bed.
He lay her down and kissed her head, moving up for a second so the two of them could look at each other's amazing bodies. Billie admired her partner's handsome firm figure, large faintly muscled arms and huge erection, while Mark stared at his partner's full and soft breasts, her cute curves and the inviting pussy between her spread legs.
After a long few seconds of hesitation, Mark moved himself downwards to prepare his insertion. A shiver shot through them both as the head of his cock kissed her clit, the two erect tips feeling amazing as they rubbed together, and surges of arousal continued to surge through them as his shaft slid down to brush against her lips and pushed between them.
Billie and Mark both gasped from the sensations of the insertion and grabbed for each other's hands as they got used to the feeling. Mark was taken by surprise by the constriction around him, and Billie was shocked by the huge insertion inside her. Thankfully there was no pain for either of them, but it still felt surreal beyond description. Mark held still for a little while, and slowly withdrew from Billie's tight hole before pushing back inside it. They both panted, but this time they smiled contentedly at each other as they felt deep arousal and pleasure from the sensations take over from surprise.
Soon Mark started to find his rhythm, thrusting eagerly into Billie and feeling her slit cling to him. Billie likewise adapted to having a cock pound her repeatedly, Mark's head brushing against a deeply sensitive point inside her and his balls slapping against her thighs, her breasts jiggling with every thrust into her and adding to the intense feelings. To her surprise, his large hands released their grip on her small ones and moved to her chest, and she moaned as he cupped the soft flesh and his fingers pinched her nipples. "You've got such nice tits, babe," Mark breathed.
Billie couldn't even try to say anything in response to that. She felt too overwhelmed by these sensations to even speak, and she could feel herself getting closer and closer to her peak. Eventually she moaned inarticulately as she hit it, or more accurately as his cock hit it and pushed her to it, and as her eyes screwed shut, her nipples and clitoris throbbed and her passage clenched tightly around Mark's cock, she was astonished by the heights of pleasure she reached. Every part of her seemed to shiver and quake from the feelings, like she could just float away.
And as he reached his own unfamiliar orgasm, Mark groaned deeply, his motions seeming instinctive and unstoppable as he thrusted the last few times. When he shot his warm seed inside her, what struck him was how while this felt less intense than a female orgasm, it felt more... climactic. All his desire seemed to be fulfilled for a glorious few moments.
Slowly coming down from their climaxes, the woman and man who had been a man and woman drifted off to sleep in each other's arms.