Erebus

Erebus is the Persona of the First Void Avatar.

Background
Erebus was the Persona of the First Void Avatar, and was unique in that it held complete dominion over the powers of Void, which is unheard of even with Nephilim. The First Void Avatar 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 the Void Avatar and sealed Erebus in Void, thus ending The First Void Insurrection.

Abilities
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, the First Void Avatar was nearly invincible, and had caused immesurable death and destruction before it was sealed by Lord Knight Falken, whose special soulcraft was able to resist Void, thereby allowing him to defeat the Void Avatar and end the Insurrection.

It is implied since Falken only sealed Erebus, that it still exists somewhere within Void, separated from its original master.