Masatomo was the 3rd son of Ashikaga Yoshinori. At first a priest, he was ordered to establish himself in Kamakura as the new kanto kubo around 1455. When this proved impossible owing to the difficult political situation in Sagami Province, he settled in Izu Province, at Horigoe Castle. He died of natural causes in 1591. He became known as the 'Horigoe kubo'.