Kokujoh, also known as Kyoshiro Kokujoh, is a recurring character in the anime Duel Masters. He is a self‑proclaimed evil genius who adopts the alias Black Reaper. His appearance is striking: tall, with long midnight blue hair, red eyes, and sharp teeth, and he almost always wears a black leather outfit and a flowing cape. Kokujoh was originally an orphan who grew up alone in Spain. At the age of ten he took refuge in the mansion of a family that guarded the Darkness civilization cards, and the family elder took him in. He lived happily with them for a time, but when he was eleven the villain Zakira and his organization Galdo attacked the family. The elder betrayed the clan to save himself, sacrificing many of its members. In a rage Kokujoh challenged the elder to a duel and killed him, afterward wandering alone as the god of loneliness and despair. He eventually made his way to Japan and joined the Duel Temple, becoming one of its Four Heavenly Kings. To create a rivalry with the temple’s strongest duelist, Hakuoh, he deliberately defeated the other three kings and set fire to the temple before leaving.

Kokujoh’s personality is cold, arrogant, and sadistic. He loves to laugh maniacally and often belittles his opponents, but he possesses a twisted sense of honor and only respects those strong enough to challenge him. His driving motivation is the pursuit of absolute power and revenge against Zakira, who destroyed the only family he had. In battle he uses a Darkness civilization deck built around Demon Command creatures and spells that eliminate enemy cards. His signature creature is Ballom, Lord of Demons, and he later employs more powerful forms such as Dorballom, Lord of Demons, and Ballom, Emperor of Demons, along with cards like Daidalos, General of Fury, Olgate, Nightmare Samurai, and Deathliger, Lion of Chaos. His ruthless, no‑mercy play style has earned him the nickname Black Death.

Kokujoh first appears as a major rival to the protagonist Shobu Kirifuda. He defeats Shobu multiple times early on, forcing Shobu to grow stronger. Despite his antagonistic role, he occasionally becomes a reluctant ally: in the second season he helps Shobu fight against the P.L.O.O.P. organization, and in later arcs he joins forces with Shobu and others to confront larger threats. His hatred of Zakira remains a constant, and he will set aside his usual lone‑wolf stance when a common enemy appears. His relationship with Shobu evolves from pure enmity to a begrudging mutual respect, and he shares a tense rivalry with Hakuoh as the two strongest duelists of their generation. Even after his initial story arc, Kokujoh continues to appear in subsequent Duel Masters series as a recurring figure, sometimes as an unpredictable ally and other times as a menace. Over time he shows small signs of growth, learning to cooperate when necessary while never fully shedding his cynical, brutal nature. In the manga Duel Masters Lost: Reaper of the Moonlight, his past is further explored, detailing his pact with the demon Ballom and the physical changes that result from it.