Cath

is Arthur Pendragon's mysterious pet that he gained after training in Istar. His real identity is, a monstrous creature born from the Mother of Chaos.

Appearance
Cath is a cat-like creature that appears to be just a small cat head with a tail. Its fur is white with red markings.

In his real form, Cath Palug is a lion-sized cat with a long tail that ends in three points, white eyes and a big mouth with sharp, misaligned fangs and a long tongue.

Personality
Not much is known about Cath's personality, as it has remained mostly silent other than sneezing at times. It prefers to stay on Arthur's head (and later his shoulder), and has refused to leave Arthur's side. Cath has the ability to talk, and has stated it is happy that Arthur is growing stronger. Cath appears to enjoy chewing on Arthur's hair and his cape.

However, when Arthur becomes the King of Chaos, Cath reveals his true colors as an evil, greedy and wild monster. He reveals that he remained by Arthur's side and protected him only to be able to devour him as soon as he awakened the power of Chaos.

History
Cath Palug was originally a creature born from the Mother of Chaos, it was reincarnated from greed and obsession for power. Its objective was to be the King of Chaos itself. The tyrant beast challenged Chaos, but lost the fight and was banished. However, Cath Palug continued its misdeeds and was eventually sealed away by the Goddess Clan. It's unknown how it escapes from the seal or how Arthur managed to find it after training in Istar.

Istar arc
After Arthur and Gowther have completed their training and return to the group, Cath is on top of Arthur's head. Merlin asks Arthur what the strange object on top of his head is, and Arthur and Gowther merely reply that it is a mystery.

After leaving Istar, Gowther tries to remove Cath from Arthur's head, but cannot do so and only ends up hurting Arthur. Gowther notes that Cath seems to be stuck to Arthur.

Great Fight Festival arc
Cath remains on Arthur's head throughout the Great Fight Festival arc.

Defensive Battle for Liones arc
Cath is still with Arthur when this, Nanashi and other Camelot knights fight against a horde of Gray Demons. When hearing it speak, Arthur is surprised and Nanashi affirms that Arthur would not die while Cath is with him. When the group is forced to retreat before the arrival of a Blue Demons horde, Cath agrees with Arthur that he must become stronger.

Prelude to the New Holy War arc
Cath along with Arthur is hidden in an underground shelter with the other survivors of Camelot. When Arthur arrives with Orlondi, Cath launches on this and keeps quiet about showing off.

Cath accompanies Arthur when he decides to go on his own to the castle of Camelot and recover the holy sword Excalibur. Being caught in the Marchen Maze of Peronia, Cath takes advantage when Arthur is attacked by a Gray Demon to approach Peronia from behind and apparently devour her.

After entering the castle, Arthur and Cath are surprised by Zeldris and Cusack. Cath decides to give Arthur the possibility of running away by levitating several objects around and attacking the demons with them. However, Cath is defeated and seriously injured.

When Arthur is able to wield Excalibur, he gives several cuts to Cusack to retrieve Cath and take him out of the castle. Arthur apologizes to him for making him suffer, to which Cath tells him he is hungry and Arthur says they will eat when they are finished.

After Arthur failed to defeat the demons, Cath points out that his magical power is still not awake and that he will not win if it does not wake up. When Arthur suffers the effects of brandishing Excalibur, Cath sends a telepathic message to Merlin warning her that Arthur will die.

When Merlin manages to remove Cusack with her Icicle Castle, Cath is teleported with Arthur to the Boar Hat in Liones. Hawk is alarmed to see him hurt but Cath insists that they must worry about Arthur. However, Arthur falls victim to Cusack's Resonant, piercing his own heart with Excalibur. Cath looks horrified to see such a fact.

When Arthur dies, Hawk tries to comfort Cath, but it is intimidated by the monstrous expression of this one.

Current arc
Cath remains next to Arthur's body in the Boar Hat, until Merlin decides to carry out Arthur's awakening as the "King of Chaos". Seeing Arthur alive, Cath rejoices and jumps into his arms, but surprisingly tries to devour him. Meliodas manages to save Arthur, but Cath ends up ripping an arm and eating it, undergoing a monstrous transformation. The Lady of the Lake tells them that they must retrieve the arm or they will soon know how powerful even a fragment of Chaos can be.

After the Lady of the Lake reveals his true identity as the monster Cath Palug, Arthur asks Cath to stop since there must be a good reason for what he is doing since he protected him with his life. However, Cath Palug reveals that he only did so that Arthur could awaken as the King of Chaos, since he would not have had a good taste by devouring him otherwise. The monster then asks an affected Arthur if he can eat him now, creating a pocket dimension with the fragment of Chaos he had devoured, sucking Arthur and the Sins in it. There, Arthur asks him what he is for him, to which Cath Palug replies that he is food that he has been waiting patiently and ask to let him eat without disturbance. Arthur then destroys the dimension with a reincarnated Excalibur. Cath Palug is amazed and asks Arthur to let him eat every part of him. Arthur says that upon hearing that, he feels he can kill him without any regret. When Cath Palug throws himself at him, Arthur cuts him with Excalibur, apparently destroying his body in pieces.

Abilities/Equipment
Cath's abilities and purpose are currently unknown, but Nanashi has stated that Arthur will not die as long as Cath remains with him.

He shows telekinetic abilities, being able to levitate multiple objects around him. He also possesses telepathic abilities, being able to mentally send a message to Merlin in Liones from Camelot.

After devouring one of Arthur's arms, Cath absorbed a fragment of Chaos itself. With it, Cath was able to create a pocket dimension in his mouth that sucks his targets inside.

Trivia

 * Cath's name is a reference to Cath Palug, a monstrous cat of Arthurian legend.
 * Arthur named it Cath after the sneeze it made.
 * It refers to itself in the first person as "Poku" presumably an old pronunciation of the first person, "Boku".
 * According to the databook(s):
 * Special ability: Not letting go of Arthur no matter what
 * Charmpoint: His roundness
 * According to his power level, Cath has the highest amount of Spirit measured accurately thus far in the series.
 * Cath would beat Hawk in a fight.