The Macrocosm. The Universe. The Multiverse. Everything. There are many names used to describe the space, matter and energy that surrounds us, the numerous dimensions and parallel worlds most imagine might (and do) exist but can never experience. I call it the Universal Realm.
No, it's not because it's the "Realm of the Universe" or anything like that. True, almost every story you've ever read or watched or heard or even daydreamed about has probably happened somewhere in the Universal Realm (see Prophetic Earth for more info), in a dimension or parallel universe most likely. Trust me, I've seen a few of those adventures happen in person. A lot of people try to encompass all of these stories and universes into one singular state, hence a lot of the terms you saw me list out at the top. I think of it a little differently though, as evidenced by the name I use. It's the Universal Realm; in other words, the realm related to everything. That doesn't mean it is everything, though.
Get ready folks, because we're going way in the past, somewhere else. Everywhere else, actually.
You see, the Universal Realm, as I mentioned, is the realm connected to everything. Which means that there has to be something for it to connect. A lot of things, in fact; a near infinite number of realms, each alien beyond comprehension, both to us and to one another. I try to give them names that more-or-less settle on a concept that defines each realm. Examples include the Realm of Fire, the Realm of Magic, the Realm of Evil, etc.
Of course, none of these names are entirely accurate. The Realm of Fire isn't really a realm filled with fire. A more accurate term may be the Realm of Temperature, since it's the only realm other than the Universal Realm with a concept of heat. As a matter of fact, it's only heat, in varying amounts that result in beings that could, in the vague-est of terms, be sentient. I said sentient, not alive; only the Universal Realm and the Life Realm contain living beings. Point is, Realm of Fire sounds cooler (see what I did there?) than the Realm of Heat or the Temperature Realm, so that's what I call it.
You may have also noticed a theme with these realms. Namely, the fact that each one seems to only share its underlying essence with the Universal Realm. That's because these endless number of realms normally never interact, completely cut off from one another. Which is good, because as weird as it would be to be in a realm of nothingness, imagine how freaked out a denizen of the Void Realm would be to stumble into the Realm of Unity.
...Assuming the Realm of the Void has denizens, that is. Come to think of it, I'm not sure how that would work. Can someone be made entirely of nothing? How would they be differentiated from the rest of empty space, without even energy, let alone matter or mass?
Sorry, I digress. Anyway, the realms never interact, with one exception. Maybe there used to be a realm of absorption that capitalized whenever there was a random breach with another realm and absorbed part of that realm each time. Perhaps there was some form of rift or explosion that ripped through every realm at once, and the energies and concepts that bled out combined and coalesced into a new realm. However it came into existence, one realm had the ability to evenly mix the concepts of the other realms into something new: the Universal Realm.
This, to the other realms, provided an interesting anomaly... and an even more interesting opportunity. While realms rarely come into contact, the occasional rift or tear between realms, whether natural or artificial in nature, allowed realms to have varying levels of awareness regarding the existence of other realms, existences that were ultimately confirmed by the emergence of the Universal Realm. Because each other realm is composed entirely of one... thing, I find it easier to see them as impossibly gigantic single-celled organisms.
This analogy works very well for another reason. Realms tend to view any of the other realms as a threat, especially those who represent a concept that is anathema to them (Light and Darkness, Unity and the Void, etc). Like single-celled organisms, they'd like nothing more than to destroy and assimilate other realms, both to remove the "competition" and to potentially absorb the essence of the other realms according the most basic survival instincts inherent to everything: consume and adapt. Usually, realms can do little more than trade a few blows when a rift opens between two realms, never causing enough damage for either to ever have a chance to succeed.
Bringing us back to the Universal Realm, other realms see us as a unique anomaly, a bridge between realms. If any other realm were able to conquer the Universal Realm, they would not only be able to absorb part of the essence from every other realm at once, it would also have a hub from which it could strike at any of the other realms with impunity. Every realm is largely aware of this, so while most realms would love nothing more than to consume us all and use us as a weapon to conquer all the realms, they are also kept in check by the knowledge that every other realm would willingly work together to prevent another realm from assimilating the Universal Realm. Think of it as a cold war, on the ultimate scale.