Demon Eyes Kyou, whose real name is Mibu Kyou, is a legendary figure known for his red, demon-like eyes and his title "Thousand Slayer" for defeating over a thousand samurai at the Battle of Sekigahara. He was ultimately defeated by a young man named Mibu Kyoshiro. After his defeat, his mind merged with Kyoshiro's, and his body was hidden in the Aokigahara forest. Kyou is sadistic and enjoys killing without mercy, although his bloodlust diminishes over time. Training with Muramasa helps him achieve greater control.
When he first meets Yuya, Kyou finds himself protective of her, though he expresses it immaturely by calling her names like "dog face" and "ugly." Despite this, Kyoshiro confirms that Kyou genuinely likes Yuya. Kyou wields Tenro, one of the "Four Great Demon Blades," forged by Muramasa and nearly unbreakable. His sword style, Mumyou Jinpuu Ryuu Satsujin Ken, taught by Muramasa, is incredibly powerful and includes techniques that can cut through air and create illusions. Later, he learns an advanced form of this style that utilizes the Four Symbols (Genbu, Seiryuu, Byakko, Suzaku, and even Kouryuu), granting him various powers.
Kyou is the last remaining True Mibu with True Red eyes, allowing him to transform into a Battle God or Demon God. Upon suppressing his battle lust as the Battle God, he earns the mark and title of Aka no Ou. Born in the Mibu village, Kyou was friends with the former Aka no Ou. When the latter turned evil, Muramasa took Kyou away to raise him as the 'hope' of the Mibu clan. Kyou traveled the world and formed the Shiseiten to become strong enough to return and defeat the former Aka no Ou. By the end of the series, he is recognized as the strongest fighter. In a bonus manga chapter, Yuya and Kyou live together.
