Lifespan: 15xx to 10/20 of Tenshō 19 (1591)
Clan: Mitoya (an illegitimate branch of the Suwabe clan from the lineage of Minamoto no Mitsuyoshi of the Seiwa Genji)
Lord: Amago Haruhisa → Amago Yoshihisa → Mōri Motonari → Mōri Terumoto
Father: Mitoya Yorisuke
Mitoya Hisasuke served as a bushō during the Sengoku and Azuchi-Momoyama periods. He was a retainer of the Amago and Mōri clans. Hisasuke was the lord of Mitoya Castle in Izumo Province. He was born as the son of Mitoya Yorisuke. Hisasuke was an owner of an invaluable tea kettle known as the Mitoya-Danjō kettle.
The Mitoya surname originated from the Suwabe clan. The Mitoya were members of the Shinano-Genji based on the lineage of Minamoto no Mitsuyoshi of the Seiwa-Genji. In the ninth month of 1221, Suwabe Sukenaga, the son of Suwabe Yukisuke, was appointed by Hōjō Yoshitoki to serve as the lord of the Mitoya neighborhood in the Iishi District of Izumo, whereupon he adopted the surname of Mitoya. After entering Izumo, the Mitoya clan followed the Enya, the Yamana, and the Kyōgoku by supporting Kyōgoku Mochikiyo (the military governor of Izumo) in the Ōnin-Bunmei War.
In 1528, Hisasuke inherited the headship of the clan from his father, Yorisuke. Initially, he served the Amago as a member of the group of samurai for the territory and his compensation was the crop yield for the Mitoya neighborhood of 6,785 koku.
in 1540, Hisasuke followed his lord, Amago Haruhisa, in an attack on the base of Mōri Motonari at Yoshida-Kōriyama Castle in Aki Province. In 1541, he was defeated by reinforcements led by Sue Takafusa, a retainer of the Ōuchi clan and Haruhisa withdrew to Izumo. Owing to this major defeat, the Mitoya clan, along with the Shinji (Shinji Takayoshi), the Mizawa, and others switched their allegiance to the Ōuchi, but, in 1543, Ōuchi Yoshitaka failed in a bid to topple the base of the Amago clan at Gassantoda Castle, and, as a result, Hisasuke, along with other kokujin from Izumo, returned to service of the Amago. Thereafter, Haruhisa endeavored to control his retainers in Izumo, granting the use of a character from his name. On 1/12 of Kōji 3 (1557), Hisasuke received one of the characters in his name, adopting the name of Hisasuke.
Hisasuke served the Amago for a while, and, in 1558, at the Collapse at Oshibara, achieved a major victory over the Mōri. In 1562, after Honjō Tsunemitsu, the lord of Yamabuki Castle, submitted to the Mōri, Hisasuke joined Mizawa Tamekiyo and Akana Morikiyo by pledging support to the Mōri. His base at Mitoya Castle served as an important logistics site for the Mōri army so Hisasuke made efforts toward its defense. In 1563, Hisasuke warded-off an attack by a retainer of the Amago named Tachihara Hisatsuna, defeating him at the Jiō Pass. Later, he participated in an attack on Shiraga Castle and the Second Siege of Gassantoda Castle. Along with Mizawa Tamekiyo and Yonebara Tsunahiro, Hisasuke served under the command of Kobayakawa Takakage in the vanguard forces for the attack on Sugataniguichi. Thereafter, the Amago clan surrendered at Gassantoda Castle.
In 1569, Yamanaka Yukimori backed Amago Katsuhisa and launched a rebellion as the leader of the Amago revival army. Along with many former retainers of the Amago, Hisasuke aimed to join the effort but was rejected by the former retainers on grounds of engaging in disloyal acts prior to the movement. As a result, Hisasuke remained with the Mōri, serving under Kikkawa Motoharu in battle at Kisaichi Castle and other locations. In 1578, Hisasuke participated in the Siege of Kōzuki Castle leading to the surrender of Yukimori and demise of the Amago revival army. Around this time, although Hisasuke submitted a written oath of allegiance to Mōri Terumoto, he refused further military service and appeared to exercise independent authority.
In 1586, Hisasuke supported the Mōri by participating in the Siege of Kokura Castle. He then deployed with his son, Takasuke, to suppress those leading the Higo Kokujin Uprising. In 1588, when his lord, Mōri Terumoto, went to Kyōto, Hisasuke accompanied him. A meeting with Tokugawa Ieyasu angered Terumoto, resulting in the seizure of Hisasuke’s territory and his expulsion.
Later, he went to the capital of Kyōto and, on 10/20 of Tenshō 19 (1591), died in the village of Yokkaichi.