@Datum I imagine the demon king noticed she would be useful for agricultural development, which might be rare among the demons if their land is indeed getting barren, unless it's climate related. Yet due to her chuuni personality she didn't ask for riches, just giving her a title was enough. So, it must have been basically a real lottery win for the demon king. I don't know what the other, real heavenly kings were like, but if they had any wits and dignity, they probably didn't care about that squirt supposedly sharing the same title, as long as she didn't disturb them. If she was governing her own small place in the boondocks and concentrating on her own stuff, she obviously wouldn't get in their way.