As the lord of the ISSHIKI -SHIKIBU family, who took in charge of Hokoshu (the shogunal military guard), Fujinaga served Yoshiteru ASHIKAGA and Yoshiaki ASHIKAGA in collaboration with Terutsune Hosokawa and so on.
奉公衆となった一色式部家の当主として、細川輝経らとともに足利義輝・足利義昭に近仕した。