In January 2010, Nagai was selected the Japan national team for 2011 Asian Cup qualification. At this qualification, he debuted against Yemen on January 6. In 2012, he was also selected the Japan U-23 national team for 2012 Summer Olympics. He played all 6 matches and scored 2 goals, and Japan won the 4th place. He played 12 games and scored 3 goals for Japan until 2019.