is a Japanese footballer who plays as a midfielder or defender for Women's Championship club London City Lionesses and captains the Japan national team. A versatile defensive midfielder with keen sense of anticipation and exceptional tactical acumen, she is also able to be deployed as a central defender. She is regarded as one of the finest Asian female midfielders of all time. She is one of the most successful East Asian footballers, of any gender, at club and international level.

Kumagai began her senior career in her native Japan with Urawa Reds in 2009. She would then move to Europe in 2011, joining Frauen-Bundesliga side FFC Frankfurt. She joined Olympique Lyonnais in the summer of 2013. Kumagai made over 240 appearances for the club, winning 19 titles trophies, including seven Division 1 Féminine titles, six Coupe de France titles, and five UEFA Women's Champions League titles. 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 left Lyon to join Bayern Munich in 2021. 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 has made over 100 caps for Japan women's national team and currently ranked as the 3rd most capped female player for the country. She made her senior international debut for Japan in 2008 at the age of 17. She had represented Japan in four World Cup tournaments, winning the 2011 FIFA Women's World Cup where she scored the decisive penalty in the penalty shootout. She had further won an Asian Games gold medal and the AFC Women's Asian Cup in 2010 and 2018 respectively. She was named captain of the national team in January 2017.