Katagai was a member of the Chōshū Ishin-Shishi under the direct command of Katsura Kogorō and a comrade of Himura Kenshin during the bakumatsu. Frequently at Katsura's side and a visitor at the Kohagi-ya, Katagai would frequently pass information to Kenshin from Katsura and is the messenger who informed Battōsai of the Ikeda-ya Incident immediately after it occurred, expressing his belief that the sole survival of Katsura himself was ordained by the heavens. For five months after the Kinmon Incident, Katagai went into hiding like most other Katsura loyalists, but spotted fellow Chōshū Ishin-Shishi I'izuka walking openly in Kyoto and followed him to a seemingly abandoned shack on the outskirts of the city. Witnessing I'izuka passing information about Kenshin's whereabouts to the Yaminobu, Katagai realizes that I'izuka himself is the traitor who had been leaking Ishin-Shishi secrets to the bakufu, but before he can escape to warn the others, Katagai is caught by Yatsume Mumyōi and killed by Nakajō, both of the Yaminobu. He was voiced by Mitsuaki Hoshino in the Japanese version.