“What is the truth?” I don’t know if there needs to be a deeper purpose. Tyrants exist in every realm. Maybe the original Cŵn Annwn set things up this way so they’d have unquestioned power. Maybe there’s some ancient reason for it, but it got twisted by mortals along the way. That sort of thing happens often enough in my realm. Religion and politics exist on a spectrum to be abused by the powerful. If there’s a universal truth across all realms, it’s probably that.
