is a Japanese competitive swimmer who swims in the individual medley, butterfly, breaststroke, and freestyle events. He won the gold medal in the 400 meter individual medley at the 2012, 2014, and 2016 world short course championships, as well as at the 2013 and 2015 world long course championships. Seto holds the world records in the 200 meter butterfly and the 400 meter individual medley (both short course).