Yuki Koike celebrated his first international successes at the 2014 Junior World Championships in Eugene , where he finished fourth in the 200-meter run in 20.34 s and the silver medal in the Japanese 4 x 100-meter relay in 39.02 s behind the United States team. The following year he made it to the semi-finals at the Asian Championships in Wuhan over 100 meters, but did not play there again. He then reached the semifinals of the Summer Universiade in Gwangju and was eliminated from the season in the first round. In 2018 he took part in the Asian Games in Jakarta for the first time and surprisingly won over 200 meters in 20.23 seconds ahead of the Taiwanese Yang Chun-han . He also won the bronze medal behind the teams from Qatar and India with the 4 x 400 meter relay in 3: 01.94 min. In 2019 he won the silver medal behind the Chinese Xie Zhenye at the Asian Championships in Doha in 20.55 seconds . At the end of September he took part in the World Championships for the first time there and reached the semi-finals over 100 meters , in which he was eliminated with 10.28 s, while he was eliminated over 200 meters with 20.46 s in the first round . He also won the bronze medal with the relay, but was only used in the run-up.
Japan
