Kumagai is a 32-year-old from Hokkaido. He was first selected for the Japan national team in 2 when he was a sophomore at Tokiwagi Gakuen High School in Miyagi.
In the final of the 2008 World Cup, which Japan won for the first time, he succeeded in winning the championship with a penalty kick. Since 2011, he has been the captain of "Nadeshiko Japan" and has been active in international matches for many years as a key defensive player.