Heinlein did a lot of stuff in his time, and I'm not convinced that his juveniles were his best work. While a lot of his later stuff is flawed -- it could have done with much more editing, and there was a period where he had medical problems -- he was tackling deeper, more complicated topics. So I thought to myself, 'Why not write a late-period Heinlein tribute? And let's update it as well. I'm about 43. Let's imagine Heinlein had been born 43 years later. He'd be about 57 now. What would Robert Heinlein's later-period novels be like, if he'd had modern medical support and had lived into the age of anime and manga, Spaceship One and Post-Cyberpunk? What would Heinlein be writing then?'
So I set out to write a modern late-period Heinlein novel. You've got to play by the Heinlein rules. To be canonical, it has to have a red-headed heroine with a nipple that goes 'spung.' This was a first and obvious anchor point. I thought to myself, 'Oh my god, how am I going to have a heroine with a nipple that goes spung?' I suddenly realized, 'Ah, it's a faulty overpressure valve, because she's a sex robot.' Then I thought, 'Hang on - but she's got existential problems.' Heinlein protagonists start off in a state of instability: something is wrong with their lives. What sort of existential problems will a female sex robot have? Well, she can't get laid because there are no more human beings. She came off the production line the year after the last human male died.