This is an abridged version of the storyline that takes place in Kingdom Under Fire: Circle of Doom. Keep in mind some characters are left out.
Inside the Dark DimensionEdit
Regnier and Kendal get trapped inside the Dark Dimension once Encablossa was destroyed. Unfortunately for them the realm is also ruled by Encablossa, and he is not too happy about his defeat at their hands. Exposure to the Dark Dimension will slowly mutate both Kendal and Regnier into Encablossa’s demons, and will eventually turn them into mindless servants to his will.
Regnier, well aware of his crimes against humanity, hoped he could go on to lead a normal life, but Encablossa had other plans. Encablossa knows Regnier is just the warrior he needs to conquer the Age of Light and to exact his revenge on Nible. As a result he will make Regnier his servant and use him to conquer Bersia. Then, he will let Regnier rule Bersia while he gets to rule the Dark Dimension (leaving Nible nowhere to go).
But first he needs to convince Regnier to fight for him. Regnier’s lose of immortality has made him subject to fear and pain, emotions that he had long since forgot. Encablossa takes advantage of this and claims he can get rid of those feelings and make him a warrior unmatched in martial prowess. All Regnier needs to do is perform a ritual to destroy the memories of his wife and child, while Encablossa will do the rest. In addition, he reveals to him that the universal stability is at risk while Nible is in charge of Bersia. So, in order to atone for his sins Regnier must save the entire universe by putting an end to the Age of Light. Regnier goes through with the plan and becomes Encablossa’s servant.
Inside the Dark Dimension Kendal encounters his friend Walter. Walter is on the verge of becoming one of Encablossa’s demons. Walters’s memories flood back to him and he pleads with Kendal to take him to his son. Kendal agrees, but first he must find Walter’s pendant to which he fused his soul. However, when he finds it he inadvertently absorbs Walter’s soul, killing him (though the game implies heavily he’s not really dead). He then promises to take the pendant to Walter’s son Thomas.
Kendal also encounters the Noble Spirit Moonlight, who has been trapped inside the Dark Dimension ever since he, Curian, Rick Blood, and Keither fought Nible during the War of Heroes. Moonlight tells Kendal that Encablossa is planning on using Regnier to conquer the age of light. Moonlight seeks to make Kendal a warrior just like Regnier, but free of Encablossa’s mind control. He wants Kendal to protect the Age of Light from Regnier. After a series of trails he succeeds in making Kendal super human.
Encablossa plans to stop Moonlight's meddle against him and reveals to Kendal the dark truth of the universe, and how he must rule in order for Bersia to survive. While Kendal believes what he is saying, he refuses to let Encablossa unleash his unimaginable horrors upon the world.
Regnier tracks down his former ally Kiether and kills him. Kiether was protecting Moonlight’s soul from Encablossa. Now, with Kiether dead, Encablossa gets to torture Moonlight’s soul for all eternity.
Regnier soon escapes the Dark Dimension and takes command of a huge Encablossan army. Kendal makes it outside the Dark Dimension shortly thereafter, although it's unclear where he is now, and what kind of army he is in command of. Both characters learn that they were inside Encablossa for a great number of years following the Encablossan War.
What happens next are the events that take place during Kingdom Under Fire II.