Kioshi Keishicho was a police officer in Japan. He was killed by the Silver Samurai during his time as a villain. In the Japanese Underworld, Kioshi was approached by Amatsu-Mikaboshi, who offered to resurrect Kioshi so he could seek vengeance on the Samurai. Kioshi agreed, and returned to Earth, bonded to a suit of armor that was the dark mirror of the Silver Samurai's armor. He became the Ebon Samurai. Kioshi sought out Silver Samurai at the headquarters of the Big Hero 6, but found that his prey had already departed the team. The Ebon Samurai joined Big Hero 6 in Silver Samurai's place, biding his time until his chosen enemy resurfaced.