The mortal realms of the Suzerain universe represent our reality - medieval times, far-flung planets, advanced societies, water worlds, monster-infested lands, post-apocalyptic ruins.... anything and everything that can exist in a physical setting. Each of them is part of the same universe from some point in history. But that history spans millennia, going further back than any historian would ever know and encompassing every future imaginable. Ancient Athens and Chicago in the Roaring '20s are both mortal realms. Our modern world is a mortal realm, in fact. It's all that we can see around us, plus its spirit world analog.
The mortal realms are split into three 'families' for easy identification:
Elements, covering the time from the end of the War to the reconnecting of the planet's quadrants.
Catalyst, covering all of mankind's history from leaving Earth to settle other places in our galaxy.