>all humans are born into sex servitude under their demonic overlords
Kind of lame, actually. A better version would be
>all individuals are born with their inherent, respected right to liberty, sovereignty, and self-determination
>obviously, with freedom comes responsibility for own actions
>the overwhelming majority of humans, they're used to rely on one another, and frankly, a lot of them are too stupid to live independently
>the demons are here to offer them accomodations, of course
>whether it's security from criminals, enforcement of traditions, communal unity, or it's social security, guaranteed employment, safety nets etc. the demons have it all covered
>obviously, the demons can't bear all the burden, so certain obligations would be laid on the human customers, citizens, subjects, tenants, servants (insert the most fitting)
<absolute majority of humans sign up for their personal preferences, literally selling themselves to the demons
Yeah, sure, some hardcore individualists would rather bear the burden of hardships on themselves. But since they and their domain are left alone, there's no need for them to try to upset things in the demon society (which they would otherwise be doing) and the whole thing works smoother than the Japanese cattle society.