Kosuke Hagino (????, Hagino Kosuke, born 15 August 1994) is a Japanese competitive swimmer who specializes in the individual medley and 200 m freestyle.
He is a four-time Olympic medalist, most notably winning gold in the 400 m individual medley at the 2016 Summer Olympics.
Hagino holds the Asian Records in the 200 m and 400 m individual medley (long course), the 100 m and 200 m individual medley (short course).
With Team Japan, he holds the Asian Records for the 4×100 m freestyle relay and the 4×100 m medley relay.
Hagino attends Toyo University, and is coached by Norimasa Hirai.
He is one of the only two Asians to have been voted World Swimmer of the Year.