To the guy who complained about names being all over the place:
MaoYuu's characters don't even have actual names; they have titles based on occupation or status. This, combined with the piecemeal scanlation release - I count at least 6 different groups, with the final 2 volumes having no fewer than 3 different translators - make it impossible to adhere to an "official" naming convention. At some point you stop giving a fuck whether it's supposed to be "Elder Maid" or "Older Maid" or whatever and trust the reader to understand. Then there's shit which is just completely wrong, like the use of "Heaven's Spire" in chapter 53. A spire isn't a stairway, it's the pointy thing on top of churches. I don't know what the TL was thinking here.
The word used for the underground demon world was 魔界 (lit. "magic world"). There's not really a 1:1 in English, so translators will take some liberties. "Spirit world", "Demon world", "Underworld", etc. are all fine. Mizukami's new manga, Saihate no Solte, uses the same word, and it was briefly translated as "Demon Realm" with nary a demon in sight before changing to "Blightlands". So it's really down to whatever makes sense in context.
As as aside, there was a naming mistranslation that appeared several times in both the official release and fan versions. For example, in chapters 45 and 54, you'll see a reference to the "House of Callichthys". The Japanese here was カリクティス (Karictis). Google turns up a genus of catfish, hence the translator threw their hands up in the air and went with that. But it was actually a reference to Rubiss Apisto Karictis, the creator goddess from Dragon Quest. The more you know.