@ShionSinX: I get where you're coming from, man, but two things:
1) This will die away to obscurity as the series develops. I forget when. Reason being is that Rem and Shera go through some crap and befriend each other and change it to having a small rivalry over Diablo's affections instead. So really, worrying about this is small.
2) The MC's true personality might be beta (which doesn't exist for humanity, by the way. Such primal thoughts don't work because of how far we advanced and evolved. Literally as worthless as saying the stars and the zodiac are what decide our destinies), but don't forget that his Demon King personality is seriously aggressive to the point the other-worlders fear/hate him, making him anything but beta. Also, he wants to protect their honor and being outed as slaves would do just the opposite, so he's using a middle ground instead.
Not trying to be a dick, just trying to clear the air.