He was the first Horigoe Kubo (Governor-general based in Horigoe, Izu Province, sometimes referred to as Horikoshi or Horiguchi Kubo),[1][2] and half-brother of Ashikaga Yoshimasa and Ashikaga Yoshimi.
He became a Rinzai monk at Tenryu-ji temple (the Ashikaga family temple) in Kyoto in his childhood,[3] but by 1457, at the age of 22, was appointed Kanto kubo of Kamakura-fu by Yoshimasa and thus forced to return to secular life.
The reason for the relocation to Izu was to challenge the authority of a shogunal enemy, Ashikaga Shigeuji.
[5] As Horigoe Kubo, he notified Yoshimasa of the "rebellion" of Uesugi Mochitomo, which caused him to lose favor with the Uesugi, who effectively controlled the Kanto region; he spent much of his time in office fighting against the Koga kubo.
[6][7] Masatomo disinherited his son Chachamaru, who would go on to murder his father during a succession dispute in 1491.