Yuuki Kouichirou (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.
Like Asuna, Kouichirou attended a private school selected by their parents and consistently retained excellent results. He was later employed to work in his father's company, RECT Inc.. Due to his connections, he was able to acquire a copy of Sword Art Online; however, he was called to an overseas business trip on the very first day of the game's official service, preventing him from trying the game on its first day. Because of this, Kouichirou agreed to lend his NerveGear to his sister for a single day, which resulted in her becoming trapped in the game for the following two years.