If demonkind isn't aggressive, I'm going guess they're the longtime guardians over some world-ending menace that humanity is (un?)knowingly trying to release by defeating the demon king.
Now I'm wondering if these girls are just exceptionally useless leeches, or if demonkind in general are pacifists who'd be genocided within months if Ralph wasn't holding the line.
I was hoping for some info about how MC ended up having to carry this title/job, but author seems set on skipping it.
My current theory is that author took a note from Japanese work ethics where you cannot quit a job once you joined the company and that's how he got tricked into it.
I didn't really pay attention to this in the first chapter. They don't kill the heroes that show up to attack and kill them? Wtf are they even doing. Are they really just waiting to die when an actual strong hero army shows up?
I'm like half convinced the demon king saw there was only one useful person to serve as a Heavenly King, selected three random fillers, and bolted a long time ago.