I have to ask what feels like kinda an obvious question now that I think about it. Is the goal to conquer ALL of althare in what I can only assume is 7 zones (seven sins seven stages each) then fight beleth right after? If I'm getting the lore right, the island is a pretty small province of a larger kingdom, and I guess it just feels kind of weird to think about one single demon taking over a single unimpressive landmass then dethroning a ruler of hell. Since at least the academy and goblin bane seem to have religious motivations, it seems a little foreshadowed that you would get your final stage by sacking their main center of worship and corrupting it.
Viewing post in "Deal With A Devil" Update!! comments
Well the imps themselves don't really have much of an interest in Althare (aside from collecting infernal artifacts), so conquering the whole thing wouldn't really matter much to them. They're all pretty eager to get back home to the Hells. Hek and Delilah would certainly have a vested interest in gaining more influence in Althare, though. So conquering the entire island isn't necessarily the goal, it would give you the best chance of becoming powerful enough to take on Beleth.
There'll be more lore drops to explain it, but Althare is technically unaffiliated with any of the larger kingdoms and lacks any kind of central government or authority. It's mostly populated by dangerous wildlife and a sleuth of independent factions (the Red Nettles being one such example). It has a lot of valuable resources, but most of the other kingdoms are doing too well off to justify any attempts to conquer it.
So while certain academic, mercantile, or mercenary groups would have an interest, most of the kingdoms wouldn't consider conquering and holding Althare to be worth the investment.
true, the island is a known hotbed for all sorts of monsters and dark worship, best not to get stuck in long insurgecy campaigns or give these groups access to the mainland by way of stow awaying. On another note, I was file diving again to see what I could find and all the bath pngs are labled base and it made me realize WAY too late that the girls are still gonna need to heal even when bathing on their own gets a little... inconvenient. Kudos to the lucky imp that gets to scrub chubbed up gremory.