An adjutant of Shinko-ryū under the command of Isurugi Raijūta, Tsukio is one of the four swordsmen dispatched to attack Himura Kenshin at the Kamiya dojo with an ultimatum: join their band or die. When he and his comrade Toji attack Kenshin together, Tsukio is immediately struck and knocked unconscious while the target agilely dodges the two-on-one strike.