Crimson Realm (NS)

The Crimson Realm (紅世, Guze) is an alternate world in which Crimson Denizen originate. Unlike in the canon when a denizen leaves the Crimson Realm they can return.

History
At the start there was no possible way to go between the world but a certain crimson lord gained power and discovered a way to cross between worlds and it led the first group of settlers on the living world. Those that arrived soon became selfish as they didn't wish to lose a part of them selves and started to attack humans for their Power of Existence. This slowly led to the destruction of the balance of the world.

At some point a way back was established by a group of Crimson Lords as a way to limit the impact of strong lords staying and eating a large amount of existence. The same group eventually became some of the core vessels that formed a contract with humans creating Flame Hazes.