The Elemental Realm
Creatures from the Elemental Realm, one of the two realms fighting to keep your realm free of the Eternals, draw their offensive and defensive abilities from the forces of nature: in particular, the four classical elements of Fire, Wind, Water and Earth. Their own civilization is likewise structured around those four elements.
Their realm was racked by long and bitter warfare, as adherents of each element fought for mastery over the others, but an uneasy truce has lasted now for many generations, a truce imposed by the need for all inhabitants of their realm to work together to battle the Eternals…or risk mutual destruction.
The Spirit Realm
Creatures of the Spirit Realm have strange powers. Some can cast a shadow across an enemy’s vision, or poison the air and water; some can project themselves astrally over long distances or through locked doors; some can transform into animals. Their society is loosely organized around various Schools of Magic, each led by a powerful practitioner of the art who draws acolytes to him or herself and trains them in the ways of his or her particular powers.
Those powers, in turn, cluster into domains of Dark and Light. Like the Realm of the Elementals, the Spirit Realm has from time to time been rent by civil conflict…but also like the Realm of the Elementals, the Spirit Realm has learned to put aside internal difficulties to battle the Eternals—and protect other realms, like yours.
The Tech Realm — Your Realm
Yours is a thoroughly human realm, a realm of kings and kingdoms, princes and palaces, peasants and prosperous merchants…and it is within these ordinary humans, though no one grasps it at first, that your realm’s unique source of power ultimately resides.
Humans are, above all else, inquisitive, seeking out what lies over the horizon, beyond the mountain, beneath the water, above the clouds. And along with that inquisitiveness comes innovation. With no magical abilities to call on, no connection to the powers of fire and water and earth and air, the people of your realm have turned instead to understanding the natural laws of the world, and turning them to their advantage. Steel can be smelted and forged into swords. Mix a few common elements in the right proportion, and you have gunpowder. Wrap a quantity of hot air inside a large envelope and you can take flight in an airship.
Always probing, always changing, always coming up with new ways of doing things, the people of your realm have created Tech, the realm’s true source of power…and eventually, they develop Tech that allows them to drain the energies of beings from other realms for their own use.
That really makes the Eternals sit up and take notice.
The Eternal Realm
The eldest realm of all is that of the Eternals. First-created, first-civilized, it has fought a never-ending war down through the eons to impose its will on all the realms that came after it, realms the Eternals see as weak, corrupted versions of their own perfect realm.
Very little is known about the creatures of the Eternal Realm, except that they are universally feared…and universally fought.