He made his professional debut on 12 April of that year in the opening league match against Yokohama Marinos at Urawa Komaba Stadium.

On 1 January 2007, he was instrumental in Urawa defending the Emperor's Cup by scoring a late winner assisted by Masayuki Okano.

In 2007, AFC Champions League, Nagai helped Urawa win the tournament scoring 3 goals.

He played all 7 matches and scored a goal in the semi-final against Uruguay and contributed to the team finishing runners-up in the competition.

He made his full international debut for Japan on 21 April 2003 in a friendly against South Korea at Seoul World Cup Stadium.