Sword Devil Executioner

Sword Devil Executioner was a member of the Monster Association.

Appearance
He had a short stringy beard and his hair was long giving him an aged look. He had 6 eyes, wore a set of spiky armor and wielded a sword of similar aesthetic.

Personality
He was a rather arrogant monster, believing himself to be an equal to Atomic Samurai. He is also very dedicated to his swordsmanship, determined to be the greatest swordsman in the world to the point that selling his own soul to his blade.

Past
Sword Devil Executioner used to be a human swordman until he sold his soul to his own blade, turning him into a Mysterious Being.

Monster Association Arc
When Atomic Samurai is killing several monsters with his Flash Attack, Sword Devil Executioner manages to block the blow. The hero is surprised by this, and Sword Devil Executioner goes on to explain his backstory and determination to kill Atomic Samurai in order to absorb his blood and become the greatest swordsman in the world. The monster then launches several swings, which Kamikaze effortlessly parries. Sword Devil Executioner boastfully claims that they are equals, but he is quickly proven wrong when Atomic Samurai slices him into several pieces, killing the monster.

Abilities and Powers
As a member of the Monster Association, Sword Devil Executioner is expected to be a somewhat powerful individual. He is also proficient with his swordsmanship, being the only one of several monsters who was able to block Atomic Samurai's Flash Attack. But in the end, he was effortlessly killed by the hero.

Physical Abilities
Enhanced Speed: Sword Devil Executioner was able to react fast enough to avoid death by Atomic Samurai's Flash Attack.

Fighting Style
Expert Swordsman: Sword Devil Executioner dedicated his life to the sword, though he was no match for Atomic Samurai.

Equipment
Sword: Sword Devil Executioner carried a sword on him and was proficient in using it. The sword is said to be empowered by his own soul.

Trivia

 * He is the first case of human turns into monster by the use of Mysticism.