In Greek mythology, Erebus was often concieved as a primordial deity, and represented the personification of darkness. In Hesiod's Theogony, Erebus is identified as one of the first five beings in existence, born of Chaos, along with Nyx, the personification of night. This is fitting for Erebus in End War Online, as it has become quite literally the incarnation of darkness and chaos.
Erebus is a humanoid Persona, posessing an overcoat that splits at its waist. It has white footless legs and white gloves, as well as a skull-like mask on top of and attached to the sides of its head to make an upper and lower jaw. Its striking feature is the eight coffins chained to its back, as well as the chains binding it to its master. Erebus wields a thin single edged blade, with its scabbard strapped to its waist.
Erebus was the Persona of the First Void Avatar, Cyratel, and was unique in that it held complete dominion over the powers of Void, which is unheard of even with Nephilim. Cyratel used Erebus to wage war on Creation, bringing Void into reality to consume all the Worlds back into nothingness, in an event now known as The First Void Insurrection. With Erebus, he was almost successful in doing so, but was stopped by Lord Knight Falken, who defeated Cyratel and sealed Erebus in Void, thus ending The First Void Insurrection.
After being sealed within Void, Erebus was reawakened by Yamato Haseo's own awakening as the next Void Avatar. Erebus began silently guiding Yamato in his realization of his Void abilities, and in time confronted him personally within Void. Erebus, in this state, is shown to be an almost omniscient and seems to hold no allegiances or ulterior motives, speaking to Yamato in a prophetic manner, and speaking of a future that even it cannot see.
According to ancient texts, Erebus held complete control over Void, and as such, was able to utilize its full power in order to infect Creation and destroy all Worlds. With Erebus, Cyratel was nearly invincible, and had caused immesurable death and destruction before it was sealed by Lord Knight Falken, whose special soulcraft able to resist Void, thereby allowing him to defeat Cyratel and end the Insurrection.
During its time as a true Persona bound to Cyratel, Erebus displayed a terrifying array of abilities, and acted in a primal and animalistic manner, outright slaughtering its enemies mercilessly and brutally, often roaring in battle frenzy and destroying anything around it in its fury.
Within Void, in stark contrast to its previous incarnation, Erebus is shown to be largely benign towards Yamato. It has claimed to possess almost complete omniscience, as it has become Void itself, and therefore sees all that was, is, and will be. However, it has said that Yamato Haseo's future is clouded to even him, indicating that his omniscience is either not complete, or that Yamato's Void nature makes him the only exception.