Demon Eyes Kyo, whose real name is Mibu Kyo, is a legendary man, known for his red, demon-like eyes, and called the "Thousand Slayer" for killing over one thousand samurai during the Battle of Sekigahara before being defeated by a young man named Mibu Kyoshiro. After being defeated, his mind fused with Kyoshiro, and his body was hidden away somewhere in the forest of Aokigahara. He is very sadistic and enjoys slaughtering anyone. Over time, his blood lust slowly decreases, though he still kills without mercy. It continues to peak at times, though training with Muramasa helps fully calm him. During this time period when he first meets Yuya, he finds himself very protective over her, though handling it in a very childish manner. Such as calling her "Dog face" and " Ugly". Though it is stated by Kyoshiro, that he indeed likes Yuya.

Kyo's weapon is Tenro, one of the "Four Great Demon Blades." It was forged by Muramasa, and it is nearly unbreakable. His sword style is The Mumyou Jinpuu Ryuu Satsujin Ken, which was taught to him by Muramasa. It teaches standard fencing skills and defense, but they are far more powerful than any of the skills of other sword styles. It is the most powerful sword school in the Mibu Clan. It utilizes attacks that can cut air and create illusions. He later learns a higher form of the style that utilizes the Four Symbols (Genbu, Seiryuu, Byakko, Suzaku and even Kouryuu), manifesting a number of different powers based upon the creatures.