It is space that lacks any value or law to it, not even time. It is not the void. It isn't empty space, because you can't "fill" it. It's space where it is physically impossible for anything to exist. A graveyard not for the dead but for the erased, a removal of anything that is. Its not death. Death implies a cycle, body, remains. its an erasure of mythical proportions. No, you can't go there. You'd be instantly erased from reality. And depending how deep you were dragged, your memory would be forgotten by all. It is what the Netherites were tasked with managing.— Miles Walker
There is only one answer to what happened to the fool hearted divine pantheon of Primordials that lays shattered among you.. Thinking they could beat Kaos' most unruly child. It makes sense. It is the boundary that determines what is and is not real. And the infinite grasping hands of the chained one sits as its conciousness. The horrific unknown. The total erasure. The horrific place that can not be named. A universal attractor. More than nothing; but the Exitium. The place that loves, yet drags the natural cycle of the great Kaos into the blank. The Daemons work tirelessly to sate his hunger; while the Archons do everything in their power to keep everything churning. Yet... Now with nature shattered-- It is no wonder reality lays dark and cold. All that is left you are already seeing. — Avernus
Abzu as described on behalf of Avernus, is a deadly, affectionate, curious, and atypical individual which serves as the oldest Primordial being save for Whysper & Kaos, as he was before reality itself, and had to exist for his other half, Brahman which serves to power existence, to come into reality.
Through various sources of the Triple Moon Goddess, Avernus, Dr.Walker, Michelle Valentine, and a anonymous tip; we have attained the following information that he is the eternal attractor. The creature is in love toxically with reality to the point of wanting to destroy it all, similar to how finding something 'cute' is actually generally a chemical aggression response.
His powerset revolves around a complete erasure of an individual from existence, but is known to give information which often makes individuals have a common response of going mad, dying on the spot, or forcing themselves to expire themselves at a later moment. Completely incomprehensibly eldritch, yet something some individuals desire for none the less.
Avernus warns against any pacts attempting to be made with the entity, as unlike the Daemon Kings, Daemons, Archons, and Archarchons, pacting with either Abzu or Brahaman will not have any terms, and merely humoring the idea of pacting with either, will suddenly allow either to overwhelm your senses, possess you, and then force you to agree to outrageous terms, which will swiftly there after end in death.
Abzu is described as being cloaked in spectral chains. Their name meaning 'Deep Water'. Avernus regales with surprisingly a classic tale of Abzu's mythology in the eyes of the Lazurinians. Often; they place them as once an individual who was allowed to wander free in preexistance. However their sadistic tendencies began to worry their parent, Kaos who observed for thirteen days and thirteen nights their child, whom rampaged across a fledgling reality, suffocating creatures with their affection and beguilings to the point where they utterly destroyed all they touched, before moving on to the next thing. It was only when their sibling Brahman was brought by Kaos, as a counterpart, something that could withstand his corruptive touch.
However Brahaman, is said in the story, to be beautiful and petite, was scared by their sibling. It took a simple touch of their fingertips to realize how disgusted by their sibling they were, as the shockwave released a massive torrent of energy referred to as the 'Winds of Magic'. And , it is in the upgust, did Brahaman flee high, high into the heavens above to get away from him. But in Abzu's panic for wanting to know this brother, they reached out to the heavens, and began to melt and corrupt reality, causing Kaos to quickly lock the primordial down deep, correcting their mistake. Keeping him as far away as possible from the other. Placing reality atop of his would be coffin, the nether, to forget about him. But their hands reach up, never forgetting that first touch, and wanting to grasp it fully.
Of course, the accuracy of this story should be taken with a grain of salt, as Primordials are never children, and none were around save for Brahaman, Abzu, Whysper, and Kaos themselves to confirm this story, which none ever have.
The reality of Abzu is uncertain, but all contact with the entity is heavily discourged, as it is unpredictable what they are capeable of.