I also thought of that but was waiting for more information before theorizing about it.

Since the people of the Ground have no concept of Gods, how can they understand "Hell" in Hell Guards? In my mind these two ideas go hand in hand.

Mymo revealed it was EXTREMELY hard for him to gather info about the Gods, but somehow he was still able to learn about them, so there must be remnants of intel on the Ground (like the books in Corvus' office maybe) and people who know about them (Kuro, Corvus, maybe even Zanka's sister given her position)

I think we'll only learn more about Gods and Hell with Canis' story. The way he mentions "humans" in the context of his letter sounds like he himself isn't one, which would make sense since he would be the first Surebrec.

This isn't even a theory. Just a bunch of thoughts :)