A Dead Apostle with 666 beasts residing inside his body.
Nero Chaos was formerly a human alchemist named Fabro Rowan who developed a means to absorb and take in the existence of various creatures to allow him to gain immortality and become a Dead Apostle. Living for over a millennium, his body has fused with 666 creatures to become a collective consciousness that while aligned with him, he lacks complete control nor comprehension over it and is slowly eating away at Nero's mind. Despite this, he wishes to learn as much about the chaos formed within his body before his mind completely fades.
Nero Chaos serves as #10 of the Dead Apostle Ancestors, the main governing body of all Dead Apostles. He is an acquaintance of Roa, as the two find themselves close enough to consider themselves friends and assisted one another with their experiments.
Nero Chaos stands at roughly 74 inches (188 cm) having gray hair and eyes. While appearing seemingly human in form, only his hands and face retain their original form as beneath his trench coat, there is a pure darkness with no visible outline as his body is seemingly made completely out of chaos.
While serious and experimentive in his former life as Fabro Rowan, Nero Chaos' mind became corrupted by the various beasts he fused with to the point where he became bloodthirsty and arrogant, considering himself to be superior to ordinary humans.
Nero Chaos is the first major threat confronted by Shiki and Arcueid as they witnessed him feeding on a number of humans through his various creatures, with Nero's goal being the death of Arcueid. His arrogance leads him to toy with and underestimate Shiki in their battle, who makes use of his Mystic Eyes of Death Perception to find Nero's origins of death and cut them, leading to the Dead Apostle's demise.
Nero's body is a collective consciousness consisting of 666 various beasts, the circumstances being owed to the Reality Marble within his body called Lair of the Beast King that allows him to absorb and fuse with the various creatures that enter his body. Under normal circumstances, a Reality Marble can only be sustained for a short period of time by its user because of the world trying to correct its unnatural presence on existence. But because Lair of the Beast King is within Nero's own body, the world doesn't consider his Reality Marble unnatural, thus he can sustain it indefinitely so long as he has the energy to do so.
Nero's body consists of various creatures from ordinary animals such as wolves and lions to even mythical creatures like unicorns and dragons. Their natural attributes are greatly enhanced while fused with his body and he is capable of using them in various ways such as using parts of their bodies to attack or eat his foes at close range, separate his body into different animals to ensnare and confuse his foe or allowing the animals to separate from his body to seek out or attack foes from a distance. Even while separated, the animals are still a part of Nero's body as destroying their physical form only returns them to his body where they are instantly restored. Because of the nature of his body, Nero is virtually immortal unless all 666 beasts within his body are destroyed all at once and the animals within it can act independently from his control. For instance, they can act on their own to defend Nero from sneak attack without his awareness should he be occupied with multiple foes.
Through his work with Roa, Nero developed an ensnaring ability called Soil of Genesis where he makes use of five hundred of the beasts within his body to put enormous pressure on their foe's body as they are absorbed into Nero's body. The ability was potent enough to entrap Arcueid during her and Shiki's fight with Nero.
As one of the stronger Dead Apostles, Nero is capable of moving through water and sunlight without risk to his life, though sunlight still weakens him to a degree. In addition, he requires large amounts of blood to sustain his body thus he normally makes use of the animals within his body to feed on many humans at once.