The most powerful demon stone, Caladbolg possesses people to become his host. Nirvana is currently serving him.
Caladbolg has no known appearance of his own; he is only seen in three bodies: Noche's, Ren's, and Jae-Hoon Chae's. He is briefly shown in the form of demonic bat wings rounded around a pair of angel wings that are closed around the stone. Other than this, there is no bodily form of his own shown as of now.
Caladborg is similar to a parasite, he possesses a host and controls their mind completely. However, there are certain points where the hosts show characterisitics that are not Caladborg related. The theory of whether Caladborg becomes the host, or takes on the host's identity and uses their memories to pretend he is the host, is still up for debate. Caladborg in Jae-Hoon's body acts like a child and is jealous of Jae-Hyuk's attention being side-tracked by Serin (whether this is Jae-Hoon's insecurity or Caladborg acting on his hosts's emotions is unknown). Caladborg is shown as insane and wishes to destroy those who stand against him. He has no issues with slaughtering innocents, he is cruel enough to play on people's fears (he tells the citizens of Abyss he will stop murdering them if they kill Serin). Caladborg has no problem on letting his host take injuries since its their bodies being hurt.
Caladbolg is asleep for a good portion of the storyline until being awakened by Mahadevi. Shortly after awaking, he begins to tear apart Urvis. He then comes under the possession of Ren, but it is soon revealed that in fact, he was possessing her. Caladborg uses Ren to sidetrack the Clan Heads as he begins to reincorprate himself into Jae-Hoon. The young boy was the true bowl, as Caladborg calls his host's body, while Ren was a protective covering used to safe-guard Jae-Hoon until Caladborg fully possessed the child. When Ren is destroyed the fushion with Jae-Hoon had finally reached completion, Nirvana steps in and takes Caladborg away to the human world.
Flashbacks of his possession of the human undead Noche depict Caladborg in the same manner as causing Noche to go power crazy and murder for entertainment.