Battle of Zenmyōtsutsumi
Date: 4/15 of Eiroku 4 (1560)
Location: Zenmyōtsutsumi in the environs of Nakashima in Mikawa Province
Synopsis: Kira Yoshiaki, the head of the Kira clan and lord of Tōjō Castle, opposed efforts by Matsudaira Motoyasu to unify Mikawa Province. After Yoshiaki’s forces attacked Nakashima Castle, Matsudaira Yoshikage led a small group of mounted soldiers to disperse them but became trapped in Kira-held territory after additional forces from the Kira joined the battle, leaving no survivors among the Matsudaira forces.
The Battle of Zenmyōtsutsumi occurred on 4/15 of Eiroku 4 (1561) in Mikawa Province. The conflict was waged between Matsudaira Motoyasu (later known as Tokygawa Ieyasu) and Kira Yoshiaki for control of the Nakashima neighborhood in the broader context of Motoyasu’s efforts to unify Mikawa after becoming independent of the Imagawa clan based in Suruga Province.
Siege of Tōjō Castle
After the death of Imagawa Yoshimoto, the sengoku daimyō of Suruga Province, at the Battle of Okehazama in the fifth month of 1560, Matsudaira Motoyasu became independent of the Imagawa clan. This led to conflict with the influential Kira clan who posed an impediment to his plans to unify Mikawa under his control.
Kira Yoshiaki assigned his base at Nanao Castle to his retainers and entered Tōjō Castle in the Hazu District of Mikawa. To the north of Tōjō Castle stood Fukōzu Castle in the Nukata District. Fukōzu was the base of Matsudaira Yoshikage, the second-generation head of the Fukōzu-Matsudaira clan. Yoshikage entered Nakashima Castle, placing a check on Tōjō Castle. In the second month of 1561, Motoyasu himself attacked Tōjō Castle, but Yoshiaki’s men put-up stiff resistance and held the castle.
Course of events
On 4/15 of Eiroku 4 (1561), Kira Yoshiaki devised a plan, assigned several hundred mounted soldiers to Tominaga Tadamoto, and had them attack Ueno Castle defended by Sakai Tadanao (a retainer of the Matsudaira). Based on instructions from Motoyasu, Yoshikage had Matsudaira Yasutada and his eldest, son, Koretada, deploy and returned to Fukōzu Castle. Yoshiaki took advantage of this opening to attack Nakashima Castle. Yoshikage immediately led fifty mounted soldiers comprised of family members and retainers who had stood guard at Fukōzu and headed toward Nakashima. After decimating the enemy forces, he pursued the Kira army fleeing in defeat. Tominaga Tadamoto, however, brought back his soldiers to give chase to Yoshikage’s contingent, severing Yoshikage’s route of return. Meanwhile, in the Kira territory, Yoshikage’s path was blocked by enemy ambushes and his forces surrounded. Fighting bravely, he cut-through the enemy and attempted to return to Nakashima, but Yoshikage along with twenty-one family members and retainers totaling thirty-four in all were killed, with no survivors returning.
Later, this site became known as the Ancient Battlefield of Yoroi-ga-fuchi. Yoshikage was killed in Shimonagara near Zenmyōtsutsumi where burial mounds remain.
At this battle, Motoyasu lost many family members and retainers, including, in addition to Yoshikage, Itakura Yoshishige (the father of Itakura Katsushige). Later, however, at the Battle of Fujinaminawate, he succeeded in expelling the Kira. Thereafter, he prevailed in battles against the Udono clan and other elements allied with the Imagawa, and, after defeating the Ikkō-ikki, achieved his goal to unify Mikawa under his control.
Moreover, Matsudaira Yoshikage was succeeded by his eldest son, Matsudaira Koretada. In the fifth month of 1575, at the Battle of Nagashino, Koretada served on behalf of the Oda in a detached unit led by Sakai Tadatsugu, but was killed in a counterattack by members of the Takeda army.
This battle is understood to have occurred on 4/15 of Eiroku 4 (1561). However, according to one account, the battle occurred in 1556. In a diary kept by a grandson of Matsudaira Yoshikage, an entry dated 3/4 of Tenshō 6 (1578) references a memorial service marking the twenty-third anniversary of the death of Yoshikage. Around the fourth month of 1556, Kira Yoshiaki betrayed Imagawa Yoshimoto in favor of Oda Nobunaga so, the character of the conflict would have changed from Matsudaira vs. Imagawa (supported by Kira) to Imagawa (supported by Matsudaira) vs. Oda (supported by Kira).
According to one account, Kira Yoshiaki’s older brother, Kira Yoshiyasu served as the head of the Kira clan at the time of the conflicts waged during the Kōji era (1555 to 1558).