Yeah, it's a really weird choice that makes no sense. Domain, sphere, field, any of those would make some sense but realm simply doesn't even slightly make sense.Ngl calling it "realm" and not "kai" is throwing me off. I watched the anime first so that's why but it's still odd to see. Especially given "realm" is a medieval term for country or territory so its a word that fits the setting well but not really in reference to a power