Ouken

Ouken (オウケン) is the former Commander of the Order 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
One of the three brothers who conspired to overthrow their father, the Brutal King of the Underworld, Ouken was a kind-hearted, loving man who wished to found an order of knights that shared his values. At some point in the past he acquired true immortality, an ability that has slowly destroyed his humanity, making him a remorseless monster that enjoys inflicting pain on others.

This madness forced Ouken's brothers to imprison him in the Underworld, where he remained until being 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.

Ouken was an enormous threat on the battlefield, easily dispatching Queen Hilling's personal guard, Anne, in a few short moves. If not for Hilling's healing magic Anne would have died. After the initial altercation Ouken began walking towards the Bosse Kingdom's capital city, presumably to murder more innocents.

Thankfully Ouken was intercepted by Desper and a detachment of the Order of the Underworld, who managed to subdue Ouken with the assistance of a massive bolt of lightning sent by King Desher. Ouken was tied up and readied for transport back to the Underworld. Everything seemed to be fine, until Ouken literally destroyed his own bones to escape his bonds, and began his counter-attack.

Demigod
Ouken is a demigod, or a human/god hybrid. In contrast to his brothers, he initially believed that he hadn't inherited any of his father's powers at all. This changed when Ouken turned 25 and suddenly found that his body would heal instantly from any injury. Ouken's power had manifested as immortality, the very ability that his father coveted.

Immortality is considered a curse in the Underworld. It's thought that if you can never die you will inevitably lose all reason to live, and will slowly descend into an endless madness. This madness has taken root in Ouken, turning him from a kind, noble man into a remorseless killing machine that lacks all reason. This lack of sanity makes Ouken uniquely susceptible to mental attack, and indeed Miranjo very easily put him in her thrall.

Ouken's body cannot be killed, and will quickly heal any wounds, even regenerating destroyed parts. This mysterious ability extends to Ouken's sword, which Ouken can reform at will, even if it's shattered. This suggests Ouken considers his sword a part of his body.

Importantly, Ouken's immortality offers no defense against magic, and indeed it's one of the few forces that can damage him for a significant length of time.

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.

Shirasampe
An initially-mysterious ability that seemed to paralyze his opponents. Ouken's "shirasampe" was later revealed to be a devastatingly simple attack. Ouken throws small pebbles at his opponent with blinding speed and accuracy, and the impact of the pebble temporarily stuns his opponent. This attack is so fast most can't even perceive it, and to date only Bojji has successfully dodged it.

Trivia
Ouken's name is a homophone 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.