His most significant rival in the breaststroke was the American swimmer Brendan Hansen. They dueled at events such as the 2005 World Championships, 2004 Summer Olympics and 2003 World Championships. Kitajima set both world records for 100 m and 200 m breaststroke in the latter occasion. Later his best in 200 m was overcome by Dimitri Komornikov and then by Hansen, who also broke Kitajima's record in the 100 m. Kitajima regained the world record (58.91) in the 100 m at the 2008 Summer Olympics. Kitajima regained the 200 m breaststroke world record in June 2008 at the Japan Open. His time of 2:07.51 shaved nearly a second off the previous record of 2:08.50 set by Hansen in 2006.