The Core Planes are three planes that exist within and alongside each other. They are the Spiritual Planes of Aetherius and Endomundo, and the Physical Realm of Nym. Their existences depend on each other, as in many ways they are of the same essences. However, only Nym is the true material plane, and it is there that all living, mortal life is meant to exist and thrive, and where everything originated from and began when the Worldshard was touched by Sol.
Of the three lesser shards that broke off from the Worldshard, one was to become Aetherius. As the broken shards melted, one piece threw itself over the larger, polished shard that was to become the planet Nym; engulfing it entirely. In time it became a sort of cloak which surrounded Nym. From Aetherius' dormant yet waking memories and the powerful energies from Nym's vast Worldsea were born the Aetherial; the First Spirits.
The First Spirits lived between the Physical Realm of Nym and the Spiritual Plane of Aetherius. As both worlds grew, their distance grew with them. The Aetherial created what they call the Spiritstone, which they placed within Aetherius. There it bonded with Aetherius' Spiritsoul, and contained it within itself. Throughout Nym the Aetherial placed large, spiritually laden stones into the ground, called Nymshards. Through these Nymshards Aetherius' Spiritsoul would be connected to Nym's Worldsoul, and so the two planes became anchored to each other.
Aetherius
is one of the two Spiritual Planes, and it is the home of the first
Guardians of Nym, who aided in the nurturing of Primordial life. For a
time the Aetherial travelled between the Physical Realm and the
Spiritual Plane frequently. They gave animals purpose and instinct, and
aided Primordials in shaping the world of Nym. Some spirits became
animals and plants themselves, and others merged with animal souls.
After the rise of the Elemental Titans, fewer Aetherial would come to the Physical Realm, deciding instead to remain in Aetherius where they could protect the Spiritstone. They decided to close off the Nymshards and limit access to Aetherius; leaving behind those spirits that remained in Nym. Other Aetherial still frequent Nym from time to time to protect the Nymshards they planted, but most will remain in Aetherius, where their desires are more locked towards the Spiritstone.
Aetherius is described as a bright, white realm of mists and clouds. Spiritual, one can say, although the mists of this plane are almost completely mystical in what they hide. Aetherius is often seen as an imitation of Nym, where its lands correspond to those of the Physical Realm. Spiritual energy gathers in Aetherius, empowered by the Spiritsoul and used to feed the many spirits of not only Aetherius, but the Physical Realm as well. Spiritual energy resides in many things in the Physical Realm, but it is only in Aetherius it is at its purest.
When
Aetherial die, they return to Aetherius to be reborn from the
Spiritsoul. Mortal souls on the other hand will enter into Aetherius
momentarily, but won't remain there as they travel towards the Great
Fade. It is in this brief moment when a soul exists within Aetherius,
Endomundo and the Physical Realm at the same time that it can be
tampered with, and in some cases be used for necromancy or resurrection.
This
shadow plane exists alongside Nym, much like Aetherius, and is bound to
the Physical Realm by Nymshards. However, only spirits in possession of
souls or infused by the Spiritsoul can make safe use of the passageways
through the Nymshards, thus more or less keeping Endomundo isolated from the Physical Realm. Endomundo imitates Nym like Aetherius does, but
it is a realm of darkness, where dark energies such as shadow and
necrotic energies are strong. Necromancers in particular draw dark
energy from Endomundo, and enslave possessed souls to create beings of
undeath.
The Elemental Titans were Shazari spirits who existed before Endomundo was created, and fed upon the elemental energies of the world and siphoned the Worldsoul to sate their hunger for energy. Since after the Elemental Titans were defeated during the War of Titans, the Creators took to control Endomundo to ensure that other Shazari couldn't somehow find a way to become new Elemental Titans.
Gaerdras was the Creator who conquered Endomundo, and to control them he created the Shadowsoul. But after Gaerdras was imprisoned as a result of his defeat during the War of Eternity, Akama took up Gaerdras' former domain and now wields the Shadowsoul. Not all Shazari yield to Akama but most do fear him. But since Creators are vulnerable when in the Core Planes, Akama risks his life every time he comes to Endomundo, as the Shazari there might plot to see him killed.
Not
all Shazari are necessarily cruel, but they grow restless and desperate
from their lack of a soul, which makes them empty inside and without
any satisfaction or purpose in existence. Their desperation to leave
Endomundo can make them dangerous, and the hunger they always feel can
lead them to witless insanity. The necrotic and shadow energies present
in Endomundo helps sustain their form and thoughts, but it is often not
enough.
When souls are travelling to the Great Fade, they must enter into Endomundo before they pass through and into Aetherius; where they again continue on to the Great Fade. It is when souls are in Endomundo that they are especially vulnerable, as the Shazari might attempt to consume or possess them. A Mortal Spirit will try to protect the soul, but it is typically drained and weakened from having spent a lifetime within a mortal.
If
a Shazari possesses a soul, it can enter into the Physical Realm,
although in some cases it is only for a limited time, and so it must
constantly seek more souls to consume to extend its physical stay. These
particular Shazari are called wraiths.
Particularly
strong souls with strong Mortal Spirits can fend off the Darkspirits
who seek to feed on souls in Endomundo, but weaker souls can be consumed
if unaided, which is why many burials use Aethra stones to empower the
Mortal Spirit and protect the soul while it is passing. Especially
fragile souls or souls that might have suffered violent or disturbing
deaths, and who do not receive proper burials, can be affected by
Endomundo's dark energies, and in some cases remain between the Physical
Realm and Endomundo as violent specters and ghosts; something which
often occurs if a soul tries to flee back to the Physical Realm, or
returns for something it might consider an important unfinished task.
Some
souls might return to the Physical Realm and re-enter their former
body; although in truth they have been possessed by wraiths, and thus
the bodies are no longer under the soul's control. Possessed souls
unable to find a suitable body become revenants; manifestations of a
fusion between a darkspirit and a mortal's soul, which might cling onto
whatever material it can find.