I have this fantasy too. It's hot as fuck.
It comes from a lifetime of being ignored by all women. And from being told that even glancing at a woman creeps them ojt and traumatizes them.
You can't imagine yourself with a woman without imagining these impossible scenarios. Since you believe you are unlovable, you believe the only way a woman would want to have sex with you is if she does something violent like raping you.
Since even glancing at a woman is now a horrible offense to them. You dont ask women out. So the only way you can imagine a woman having sex with you is if she initiates everything. Of course, you'd say no at every step, because if you hint that you're into her you're automatically a rapist.
Virgins think a hot woman raping them. Or them suddenly waking up on a fantasy land of cartoon elf maidens. Is more realistic than them getting normal girlfriends