Ashikaga Fujimasa served as a bushi during the Azuchi-Momoyama period.  He was the third son of Ashikaga Haruuji, the fourth Koga kubō based at Koga Castle in Shimōsa Province.

The details of Fujimasa’s movements up until the end of the Eiroku era (1558-1570) are unknown, but it is expected he was operating with his older brother, Ashikaga Fujiuji, and younger brothers, Teruuji and Iekuni.  Similar to Fujiuji, Fujimasa received one of the characters in his name from Ashikaga Yoshifuji (later known as Yoshiteru), the thirteenth shōgun.

Following the death of Fujiuji, he served as his de facto successor, and with the support of the Satomi clan of Awa Province, sought action from multiple clans in the northern Kantō Region such as the Satake and Utsunomiya to wage a campaign to restore his family’s position as the Koga kubō.

Fujimasa is known to be living until the end of 1572, but his whereabouts thereafter are unknown.  Under one theory, he may have been forced to kill himself by the Gohōjō in connection with the Third Battle of Sekiyado in 1574.