Lifespan: 1/17 of Daiei 4 (1524) to 6/20 of Keichō 3 (1598)
Other Names: Banryūsai (monk’s name)
Rank: bushō, daimyō
Title: Junior Fifth Rank (Lower) and Governor of Ise
Lord: Yūki Masakatsu → Yūki Harutomo
Father: Mizunoya Harumochi
Siblings: Masamura, Katsutoshi
Wife: Kotōhime (daughter of Yūki Masakatsu)
Children: Daughter (formal wife of Yūki Harutomo)
Mizunoya Masamura served as a bushō and daimyō during the Sengoku and Azuchi-Momoyama periods. He was a retainer of the Yūki clan and is counted among the Four Guardian Kings of the Yūki. Masamura served as the lord of Shimodate and Kugeta castles in Hitachi Province.
Similar to the Yūki, the Mizunoya were descendants of Fujiwara no Hidesato, a noble and bushō of the Fujiwara-Hokke from the middle Heian period in the tenth century.
In 1524, Masamura was born as the eldest son and lineal heir of Mizunoya Harumochi, a retainer of the Yūki clan. He received one of the characters in his name from his lord, Yūki Masakatsu, and adopted the name of Masamura.
As the lord of Shimodate Castle, and known for excelling in the military arts, Masamura was invited by Masakatsu to become his son-in-law and he was known as one of the Four Guardian Kings of the Yūki. Masamura engaged in battles against relatives in the neighboring territory to the north of the Shimotsuke-Utsunomiya clan. He built Kugeta Castle on the front lines of the battle along the provincial border with Shimotsuke and, after becoming its lord, made numerous contributions on the battlefield. Below Kugeta Castle, he fostered the production of cotton fabrics for which the Mooka area was well-known and he established a distribution network via marine transport on the Gongyō River. This served as the foundation for the later development of Shimotsuke-Kugeta and Hitachi-Shimodate.
In 1544, he attacked Nakamura Castle held by the Utsunomiya clan, killing its lord, Nakamura Genkaku, and toppling the castle. On 3/10 of Eiroku 9 (1566), owing to his contributions to restore territories under the direct jurisdiction of the Imperial Court, and through his nomination by a noble named Yamashina Tokitsugu, Masamura was invested with the title of Junior Fifth Rank (Lower) and Governor of Ise. In 1569, he transferred headship of the clan to his younger brother, Mizunoya Katsutoshi, and entered the priesthood, adopting the name of Banryūsai.
Later, to oppose the Gohōjō clan who invaded the northern portion of Shimōsa from a foothold in Musashi Province, Masamura aimed to form an alliance between the Yūki and Satake on one hand along with the Tokugawa and Nasu clans. In 1585, during the capture of Tano Castle in Shimotsuke Province, just before the fall of the castle, Haneishi Tokimasa (the lord of the castle dispatched by the Kasama clan who were retainers of the Utsunomiya) launched a final charge, engaging Banryūsai in a one-on-one duel. Banryūsai prevailed and the castle fell. As recognition for his efforts, Banryūsai received landholdings in Tano with a value of 400 kan.
In the fourth month of 1586, Masamura attacked Imaizumi Yasumitsu, a retainer of Utsunomiya Kunitsuna, at Kaminokawa Castle, but could not overcome an army led by Kunitsuna, Haga Takauji, Nagayama Michie, and Nakamura Tokinaga so Yūki Harutomo reached a settlement on the condition that he transfer a portion of the Nakamura territory to the Utsunomiya. In the seventh month, Masamura served as a proxy for Harutomo who was ill, participating in the conquest of the Mibu clan by Satake Yoshishige and Utsunomiya Kunitsuna. After the Conquest of Odawara by Toyotomi Hideyoshi, Masamura rose to become a daimyō independent of the Yūki clan and established the foundation for the later Shimodate domain in Hitachi.
Masamura died in 1598.
According to one account, he suffered from an ailment to his left eye but possessed a noble presence.