Here’s what you need to know about Cavalier of the Abyss manhwa:
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.