Lifespan: 15xx to 6/2 of Tenshō 3 (1575)
Rank: bushō, daimyō
Title: Secretary for Maintenance
Father: Mimura Iechika
Mother: Daughter of the Awa-Miyoshi clan
Siblings: Shō Motosuke, Motochika, Motonori, Sanechika, sister (wife of Ueno Takanori), sister (wife of Narasaki Motokane), Ryōjuin (formal wife of Mizuno Katsunari), sister (wife of Ishikawa Hisanori)
Mimura Motochika served as a daimyō during the Azuchi-Momoyama period. He was the lord of Bitchū-Matsuyama Castle.
Motochika was born as the second son of Mimura Iechika, a daimyō in Bitchū Province. Backed by the Mōri clan, Iechika garnered control of almost all of Bitchū in addition to a portion of neighboring Bizen Province. Iechika aimed to expand his influence further into Bizen as well as in Mimasaka Province, but upon concluding a frontal attack was impossible, in 1566, Ukita Naoie arranged for Iechika to be assassinated by Endō Hidekiyo and Endō Toshimichi (siblings).
Prior to his death, Iechika’s eldest son, Shō Motosuke, had already been adopted by the Shō clan in Bitchū so Motochika inherited the headship of the Mimura clan from his father. Aiming to exact revenge against the Ukita clan, in 1567, Motochika led an army of approximately 20,000 soldiers to invade Bizen, but, at the Battle of Myōzenji, were roundly defeated by a contingent of only 5,000 Ukita forces. This outcome led to a decline in the authority of the Mimura family in Bitchū, marked by events such as the betrayal of Ueki Hidenaga, the lord of Saita Castle, to the Ukita. Nevertheless, with the support of the Mōri, Motochika was able to keep in check the forces against them.
Conflict with the Ukita clan
In the twelfth month of 1569, Motochika deployed with forces along with reinforcements from the Mōri including Mōri Motokiyo and Kumagai Nobunao with the intention of subduing Ueki Hidenaga following Hidenaga’s betrayal of the Mimura in favor of the Ukita. This contingent, however, suffered a loss at the hands of Togawa Hideyasu who had been sent by Ukita Naoie. Motochika himself incurred injuries and was forced to retreat. In the first month of 1570, Akiage Tsunahira of the Amago Revival Army aligned with Naoie and charged into Bitchū. Shō Takasuke and Katsusuke (father and son) of Matsuyama Castle and Ueki Hidesuke (the son of Hidenaga) supported him and rebelled, attacking Kōzan Castle defended by Ishikawa Hisanori. Meanwhile, Hosokawa Dōkun of Sugiyama Castle was also defeated, resulting in precarious circumstances for Motochika. In the second month of 1571, Motochika took advantage of the absence of Shō Katsusuke to join Mōri Motokiyo in an attack that killed Shō Takasuke and enabled the recapture of Bitchū-Matsuyama and Sarukake castles. Riding the momentum, Motochika attempted to recapture Saita Castle, but was blocked by Shō Katsuske and Ueki Hidesuke and failed.
In the ninth month of 1571, when Motochika joined with his older brother, Shō Motosuke, and his uncle, Mimura Chikanari, for another attack on Saita Castle defended by Ueki Hidenaga, he was defeated by reinforcements who came in support of the defenders, led by Okamoto Hidehiro (a retainer of the Uragami) and Oka Ietoshi (Buzen-no-kami) and Hanabusa Motohide (retainers of the Ukita), while Motosuke died in the battle.
Later, in 1574, the Mōri clan joined with their mortal enemy, Ukita Naoie, so Motochika overcame the opposition of Chikanari and some of his senior retainers including members of the Takei clan, colluded with Oda Nobunaga, and abandoned the Mōri. He further aligned with Uragami Munekage and Miura Sadahiro after their defeat to Naoie at the Siege of Tenjinyama Castle that lasted from the fourth month of 1574 to the ninth month of 1575.
The Mōri considered the separation of Motochika as a significant event. Kobayakawa Takakage argued for an operation to subdue the Mimura, but Kikkawa Motoharu advised against an attack and instead advocated for a direct meeting with Motochika to understand his true thinking. Takakage himself had also been against joining forces with the Ukita. However, Takakage had responsibility for the Sanyō area, while Motoharu managed the Sanin area, so his counsel was not accepted and a decision made in favor of Takakage. In the eleventh month, an army to subdue the Mimura was quickly assembled and, from Izumo Province, Shō Katsusuke and Ueki Hidesuke invaded Bitchū and attacked Saita Castle, triggering the Bitchū Conflict.
The main division of the Mōri army invaded Bitchū in the middle of the eleventh month but, owing to defensive measures taken by Motochika, did not attack Motochika’s base at Bitchū-Matsuyama Castle. Instead, the invading forces adopted a strategy to attack and topple the outlying castles intended to protect the surroundings. By the end of the month, the forces toppled Yuzuriha Castle, compelling Motochika’s younger brother, Mimura Motonori, to take his own life. Thereafter, the Mōri army continued the assaults and, on 12/23, Mimura Hyōbu gave-up defending Sarukake Castle and retreated to Matsuyama Castle. On 1/1 of 1575, Kuniyoshi Castle fell followed, on 1/20 by Minagi Castle and, one 1/29, by Kinomi Castle. After capturing the outlying castles, the Mōri army surrounded Bitchū-Matsuyama Castle and, on 3/16, attacked, but, owing to losses, decided to change their plan to wait-out the defenders. In the fourth month, the besieging forces cut-down the crops in a broad area of Bitchū to the border of Mimasaka Province. Isolated and without prospects for reinforcements, some of the defenders began to betray Motochika. On 5/22, Matsuyama Castle fell. Motochika, together with his wife, children, and retainers, made an effort to flee, but then resigned himself by sending a servant to the Mōri army to request that he commit seppuku before a messenger. The Mōri acknowledged the request and, in front of an old acquaintance from the Mōri family named Awaya Motokata, left behind a death poem and took his own life on 6/2 in the Shōren Temple.
Motochika was known as a cultured individual who appreciated a sense of refinement and was well-versed in traditional poetry. He had friendly relations with Hosokawa Yūsai who was admired for his knowledge of cultural arts ranging from poetry and tea ceremony to period drama and cuisine. While Yūsai was holed-up in Bitchū-Matsuyama Castle, he gave a compilation of works to Motochika. In connection with taking his own life, Motochika gave a verse to Yūsai. Later, Motochika’s son, Shōhōshimaru was captured, and appeals were made to spare him, but Kobayakawa Takakage feared his intelligence so he was killed. As a result, the bloodline of the Mimura as a sengoku daimyō family came to an end with Motochika’s uncle, Chikanari, the only survivor, serving as a retainer for another family.
Motochika has several graves including at the Genjū and Raikyū temples in present-day Okayama Prefecture.