Born in 1967, Yagi grew up during the boom of tokusatsu television shows in Japan.
He made his directorial debut on the fourth episode of the TV mini-series Moon Spiral in 1996.
Around the same time, he also began work on his first feature film, Superior Ultraman 8 Brothers.
Yagi retired from Tsuburaya Productions in January 2008 to pursue a career as a freelance director/producer.
His first directorial piece after leaving Tsuburaya Productions was Toei's Urban Legend Sepia.