Lifespan: 14xx to Eishō 1 (1504)
Title: Govenor of Chikugo
Bakufu: Muromachi – deputy military governor of the eastern portion of Sanuki Province
Lord: Hosokawa Masamoto
Father: Yasutomi Mototsuna (?)
Siblings: Motoie, Wakatsuki Mototaka, Hideharu
Children: Motoharu, Motoaki, Uragami Sukemune
Yasutomi Motoie served as a bushō from the latter part of the Muromachi period to the Sengoku period. Motoie was the kasai, or head of house affairs, for the Hosokawa-Keichō family. He was also known under the names of Matasaburō and Shinpei-no-jō.
Motoie was a member of the Yasutomi clan serving as senior retainers of the Hosokawa-Keichō family (the main branch of the Hosokawa), inheriting the role of deputy military governor of the eastern portion of Sanuki Province in Shikoku and the landholdings. His younger brothers included Yasutomi Wakatsuki Mototaka who was known as Yasutomi Minbu-no-jō and Yasutomi Hideharu who served as the abbot of the Shinnyo Temple in Kyōto. Motoie and his siblings are surmised to have been the children of Yasutomi Mototsuna.
From around 1470, as the head of the Yasutomi clan, Motoie served as the deputy military governor of the eastern portion of Sanuki. As the head of house affairs for Hosokawa Masamoto, Motoie attended to Masamoto in Kyōto. Masamoto held the significant role of kanrei, or deputy shōgun of the Muromachi bakufu. During this period, while supporting Masamoto, Motoie served valorously in numerous battles across the Kinai.
In 1491, after Masamoto was appointed as the military governor of Ōmi Province, Motoie became the deputy military governor, whereupon he headed to Ōmi to govern the province. In 1493, after the Meiō Political Incident, a coup d’état orchestrated by Masamoto resulting in the ouster of Ashikaga Yoshiki (later known as Yoshitane), upon orders of Masamoto, Motoie joined with Uehara Motohide to attack and eliminate Hatakeyama Masanaga at the Shōgakuji Castle.
At the time, Masamoto was preoccupied with shūgendō, a form of mountain asceticism incorporating Shintō and Buddhist concepts, and did not take an interest in governing, so the Hosokawa-Keichō family conducted affairs of the bakufu through a council of senior retainers referred to as the uchishu, or inside group. As the head of this group, Motoie conducted affairs of governance on behalf of Masamoto, and, in fact, managed affairs of the bakufu. Masamoto had no wife and three adopted sons, Hosokawa Sumiyuki, Hosokawa Sumimoto, and Hosokawa Takakuni. The absence of a natural successor created tensions within the Hosokawa-Keichō family with respect to who should be the designated successor to Masamoto. Motoie backed Sumimoto as the successor. In 1504, Motoie died in battle against Teramachi Matasaburō in Yodo in Settsu Province.
On 6/23 of Eishō 4 (1507), in an event known as the Lord Hosokawa Incident, Masamoto was assassinated by retainers backing Sumiyuki as the successor, leading to a violent power-struggle as factions backing each of the adopted sons vied for control.
On 8/1 of Eishō 4 (1507), Yasutomi Motoharu, Motoie’s eldest son who inherited the role of deputy military governor of Sanuki, was killed in action in connection with the internal conflicts in the Hosokawa clan. Moreover, in 1511, at the Battle of Funaokayama, Yasutomi Motoaki who was managing the Yasutomi clan after the death of Motoharu, was also killed in action. Owing to the succession deaths in battle of Motoharu and Motoaki who were the successors to Motoie, the main branch of the Yasutomi clan lost its influence in the Kinai and at once collapsed.
Above matters of governance, Masamoto demonstrated a deep interest in shūgendō, a form of mountain asceticism incorporating Shintō and Buddhist concepts. Consequently, Motoie often performed affairs of governance on his behalf and became the real holder of authority in the family, exercising his power to the extremes.
On the pretext of practicing shūgendō, Masamoto traveled to Tanba Province and did not endeavor to return to Kyōto so Motoie, along with Shō Motosuke, headed toward Tanba and forcibly brought Masamoto back to the capital.
The appointment of Motoie as the deputy military governor of Ōmi Province was connected to the subjugation of Rokkaku Takayori (a sengoku daimyō and the twelfth head of the Rokkaku clan) by Ashikaga Yoshiki (the tenth shōgun of the Muromachi bakufu) in an event known as the Chōkyō-Entoku Expedition. As a result, Motoie’s efforts to govern Ōmi were notably hindered by guerilla attacks by surviving remnants of the Rokkaku. In a bid to gain control, Motoie, with the support of Oda Toshisada and Uragami Norimune, engaged in assorted battles in the province. In the ninth month of 1492, he petitioned to resign from the role as deputy military governor and returned to Kyōto.
In 1502, Masamoto had a falling out with Ashikaga Yoshizumi and shut himself in Motoie’s residence. This provided further evidence of the absolute trust that Masamoto had in Motoie.