unrelated but had an idea you might like
- futa orc schemes to improve herself for her lover
- pretends to be an ally to an elven mage, and lures them into a 'trap'
- the trap swaps their bodies, and the orc, now in the elf's body, seduces the elf in her old body.
- while doing so, she takes medicine she stashed at the site and swallows it
- they start to fuck, and while the elf is in the throes of passion, her former body starts to melt and spread across her.
- the elf cums inside her former womb, right as her old face latches onto the orc's face - and completely envelopes her.
- she struggles for a moment, but the pleasure is too much, and she gives in
- the orc fully takes over, turning her old body into a new, muscular, extremely curvy elven one, and absorbing the elf's memories in the process.