Koichiro Yuuki (結城浩一郎, Yūki Kōichirō) is a minor character throughout the Sword Art Online series. He is the older brother of Yuuki Asuna and would have been one of the 10,000 players to be trapped in Sword Art Online (SAO), if circumstances had not forced him to depart on a business trip on the first day of the game's official service.