If she's the most desirable person to fuck then why is she initiating all the fucking hahaha.
Sounds like if you want the gameplay to match the story then she might just have a huge robot kink or the 20% human part is mostly the genitalia. Maybe there's no more human men in the world and the population is declining and she's going around trying to find a suitor or something.
Maybe she's 80% robot and everyone else is 80% human which makes them the most desirable to fuck since she is afterall doing the fucking in the gameplay. Well whatever you figure out in the story I'll be looking forward to it!