You mentioned half devils earlier being a viable race provided they can hide what they are, what would that kind of character entail? And on a similar note, demons themselves, these the sort of demons that are basically just humans but look monstrous, are they actually evil creatures? I'm guessing evil creatures given the summary, but you never know. If evil, what sort of evil? Are they like frieren demons, predators that evolved to imitate humans to better prey upon them, that feel entirely different emotions than humans do, or a more traditional fantasy demon? 

If a half devil was born with/ended up growing large horns, would it be viable to cut them down to a point where they could be hidden in hair? If that was done, would that have any sort of long term effects and consequences on that half devil? Like if it turns out that devil horns are key factors for devils to use like magic or something, or something like constant headaches from having to cut off their horns often due to them trying to regrow, if thats something the horns could do? 

What is the awareness of the kingdom of the demon king and his army, wha  t do they know of them and what do they think of them? What happens to any demons or half demons found inside the kingdom? How do demons interact with that miasma that a lack of mana results with? How would half devils compare physically with humans? Do demons have their own religion and if so do we know anything about it? How many kinds of demons is the kingdom aware of? Any of particular note besides the demon king?

Also a little unrelated, what's the royal family of luzia like? How many princes and princesses, and are any of them of particular note? What're the reigning king and queen like? Are any of those mentioned vassal families worth knowing about?