I could be over looking this information in the rule book, but how exactly is a regent appointed their position? Is it done by the leaders of the original four kingdoms or is the title passed down through bloodline?
In my mind, historically speaking, the Supreme Regent is appointed their power through an office of successions, governed by a vote from the inner council, a group of high-ranking noble-like officials that have the job of carrying out the decisions of the Regent. However, this is the sort of nuance that I don’t necessarily want to dictate as a “rule” per se. However you envision it makes the most sense to you for an empire to be governed by a sovereign ruler is how it should be for that campaign. Perhaps it’s something more similar to the emperors of ancient Rome, or perhaps it’s more like a republic. Your call.