[1] A versatile defensive midfielder with keen sense of anticipation and exceptional tactical acumen,[2] she is also able to be deployed as a central defender.

She was part of the squad that won 4 continental treble of Division 1 Féminine, Coupe de France, and UEFA Women's Champions League in 2015–16, 2016–17, 2018–19, and 2019–20.

She won the league title with Bayern Munich in 2022–23 season before joining Serie A side AS Roma in the summer of 2023.

Kumagai scored the decisive penalty for Lyon in the 2016 UEFA Champions League Final, following a player-of-the-match performance.

[6] The following month, on 12 May 2021, Kumagai would return to the Frauen Bundesliga when FC Bayern Munich announced her as their first signing of the season.

In 2011, she was part of Japan's World Cup-winning team, scoring the winning penalty in the final against the United States.

On 10 November 2019, Kumagai scored her first ever goal in a friendly match for Japan in a 2–0 win against South Africa.