Ouken

Ouken is the former Commander of the Knights of the Underworld, a member of the Underworld royal family, and such a fierce warrior that he's known as the Sword King of the Underworld.

He was imprisoned in the Underworld until being freed by Miranjo.

Appearance
Ouken is a somewhat tall, thin man who wears head-to-toe plate armor with shaggy black hair running down his back and a shaggy black pelt around his waist. Rather than a normal visor, his helmet features an intricately-wrought face with a strange, slightly puckered mouth, completely black eyes, and long devil horns protruding from its top.

Personality
Ouken appears to be deeply disturbed, and seems to relish acts of violence so much that he trembles in anticipation of doing them. Moreover, after attacking an opponent, Ouken likes to crouch down and observe them as they die, refusing to deal a killing blow.

Prior to this Ouken was a kind and peaceful man, who is remembered fondly by those that knew him.

Plot
Ouken is one of the Underworld prisoners freed by Miranjo to conquer the Bosse Kingdom.

While all the prisoners are notorious in their own right, those familiar with Ouken seem to openly fear him, and it's suggested that he is, by far, the most dangerous of the group. He easily dispatched Kingbo, another prisoner who was a former King and a very capable warrior, in a brief altercation.It has been revealed that Ouken is actually the brother of King Desher and Desper, and was once a kind, loving man until his soul was corrupted by immortality.

Master Swordsman
Ouken is a master swordsman, and was considered the pinnacle of swordsmanship in the Underworld. His title, "Sword King of the Underworld," suggests he is at least as powerful as a king, and may have been a literal king himself.

Freezing/Paralysis
Ouken has demonstrated the ability to freeze a person in place with an invisible, distanced attack. The extent and nature of this ability, whether it's psychic or magical, is currently unknown.

Immortality
Ouken is a true immortal, a being that cannot be killed by any known object or force. His body can be injured, but will regenerate quickly, sucking back any spilt blood and regenerating destroyed parts. This power has slowly destroyed Ouken's soul, making him incapable of feeling empathy or remorse for anyone or anything.

Trivia
Ouken's name is a romanization of the Japanese words 王 (Ō, meaning king) and 剣 (Ken, meaning sword). It's possible that the name Ouken is just shorthand for his full title, "Sword King of the Underworld." However, this is unconfirmed.