Cavalier of the Abyss (심연의 카발리어) is a Korean manhwa series written by Juder.
It is the sequel to Immortal Regis. Reading the entirety of the prequel is highly recommended, otherwise, this story from chapter 4 on will spoil it and/or be confusing.
Cavalier of the Abyss (so far) is set only in the world of Chaos. There is now a Regis of Chaos.