Remember that day? You asked me what was it that made this realm unique to ours. For that, all I need to say is tilt your head and look up into the night sky. Look up at the twinkling of every star and every streak of light passing by. Reach out your hand and try to grasp the moon. Embrace it, because this is as close to the moon or stars we will ever be.
But mortals, the humans...they can venture forth into the great unknown. Imagine it. Being able to step foot onto alien worlds dissimilar to any of the divine domains. Being able to float among the stars, a speck in an endless void surrounded by the brightest and greatest beacons in the Universe. To be able to walk where the 5 once did.
I have my pride as a devil, but sometimes, I truly wish I was born human. What I would give for just an opportunity to be up there. They do not even realize what a paradisal life they get to live. They do not realize how lucky they are for such opportunities that every other species can only dream of.
But...then if I were human, perhaps you wouldn't be here, sitting next to me and listening to my rambling.
Aviinzil, Inur. Mortal Year 2010, while on a date on Earth
Among the seemingly infinite numbers of planes of existence, there is the one that came before all: the Mortal Plane. The Mortal Plane was and is the first of the Planes, created by the 5 Primordials shortly after the Singularity Bursting event. The Mortal Plane is used interchangeably with The Mortal Realm and simply Earth, as life in the plane is only known and found on the planet.
A Unique Among Uniques
Unlike any other plane, the Mortal Plane is unbound to any physical law because it is its own physical law. At times the plane's physical law comprehensible and at others, incomprehensible and acting of its own accord.
Found in the Mortal Plane, existing on a pale blue dot, is perhaps the most unique of species. Humans. In recent millennia, deities and those living in other planes have acquired fascinations with the human race for a variety of reasons. Many deities have shown such fascination that they, at several points in the Earth's history, revealed themselves to the humans. As a consequence, humans began worshipping the deities. However, because of the humans' willingness to accept and revere deities, this led to many of the divines to fight for rule over Earth.
After the 4th Great Holy War, the Mortal Plane was declared to never once more be allowed to be under the rule of deity(ies). Already unique in the fact that the Mortal Plane could be allowed multiple pantheons to rule it, it also became unique in never being allowed to be ruled by any. Interestingly enough, however, there are still a handful of pantheons that indirectly interfere with the lives of humans without breaking the Law of Complete Neutrality.
The Mortal Plane is also the only plane that has no confines. Every other realm has "Plane Boundaries," which separate it from the Mortal Realm.
Mortals, Cosmos, and the Afterlife
Humans have the shortest lifespans of any of sentient species in the Universe. Because of this, they are frequently referred to as "mortals" for their short lifespans in comparison to the much longer of other species. For this reason, as well as the Mortal Plane having no Plane Boundaries, humans are the only known species in the entirety of the Universe to be able to venture into the cosmos. This has created envy among other species as the study of the cosmos is a popular subject in many other planes of existence.
Unlike any other species, humans are capable of living an afterlife should they meet certain criteria. These afterlives occur in a separate plane, where they resurrect as a pseudo-species of whichever plane's inhabitants live in e.g., angels in Paradiso or devils in Infernus. Such an allowance has also led many to flock to the "mortals" for tales of the cosmos, a prevalent misconception that many have of humans all being cosmologists.
The Law of Absolute Neutrality
The Law of Absolute Neutrality is the only divine law that governs the Mortal Plane. It was created by The Fifth and Chronos, with Ri'ful'dan and Zan'nal'takriin only agreeing with its enaction after deep reflections of their actions in the 4th Great Holy War. The Mortal Plane can not have any deity ruling any part of the Plane, and absolutely nowhere on Earth. This means deities can not have a direct influence on the lives of humans. The law should it be broken, has severe punishments such as allowing The Great Enigma to devour an entire Pantheon's divine domain or the start of another holy war.
The Law exists not only to protect humans but the Plane as well. Also due to the law, the Mortal Plane additionally allows humans to have faith in whatever pantheon any individual chooses without repercussion like before the law. There is a loophole that allows pantheons to indirectly influence the lives of humans. This only affects their afterlives and not the one they live in the mortal realm, which technically does not violate the law.
This law allows a pantheon to "claim" the soul of a mortal should they meet certain criteria. And even then, the number of souls that are claimed are minimal. Souls claimed are usually special cases and are allowed passage into whichever realm that claimed them, regardless of their faiths or judgment in the Judicium Realm.