In 1998 season, he made his Pacific League debut and pitched in seven games.[3]
In 1999 season, He and Junji Hoshino, who was drafted the same year, won 10 games and contributed the Fukuoka Daiei Hawks win their first Pacific League championship.[4] In the 1999 Japan Series, Nagai started Game 3 and won without allowing a run in 6 innings. For this performance, he received the Japan Series Outstanding Player Award.[2]
Nagai pitched in 96 games in 8 seasons overall, compiling a 28-21 win–loss record record and a 4.67 ERA.[3]
After his retirement, Nagai has worked as a front-office officer for the Fukuoka SoftBank Hawks since 2007 and was appointed assistant deputy general manager of the team's general headquarters in January 2017.[5] On December 1, he became the general manager of the team headquarters division, organizing and development department and the head of the development department scouting office.[6]
On December 1, 2018, he was appointed general manager of the organization and development division of the team's general headquarters and general manager of the scouting and development department.[7]
On June 1, 2021, Nagai was appointed to the position of Executive Officer in addition to his current position.[1]