Battle of Nakatomigawa
Date: 8/28 to 9/21 of Tenshō 10 (1582)
Location: On the shores of the Nakatomi River and in and around Shōzui Castle in Awa Province
Synopsis: The unexpected demise of Oda Nobunaga in the sixth month of 1582 meant the loss by the Miyoshi clan of Awa Province of their primary patron and counterweight to Chōsokabe Motochika, the sengoku daimyō of Tosa Province. This created an opportunity for Motochika to attack Sogō Masayasu in Awa in pursuit of his broader ambition to unify all of Shikoku. Despite setbacks including a major flood, his larger army eventually prevailed after a chaotic battle that yielded many casualties on both sides.
The Battle of Nakatomigawa occurred from 8/28 to 9/21 of Tenshō 10 (1582) in the environs of Shōzui Castle and along the shores of the Nakatomi River in Awa Province. This conflict was waged between Chōsokabe Motochika, the sengoku daimyō of Tosa Province, who aspired to control Awa Province, and Sogō Masayasu, based in Shōzui Castle. Masayasu was joined by the lords of other castles in Awa aligned with the Miyoshi clan. The conflict lasted for approximately twenty days, resulting in the most casualties from a battle in the history of Awa Province.
In the fifth month of 1582, Oda Nobunaga assembled forces for an invasion of Shikoku, assigning Miyoshi Yasunaga to lead the vanguard forces and Nobunaga’s third son, Oda Nobutaka, to serve as the commander-in-chief of this army. News of these preparations caused Motochika to temporarily pull-back forces which had already advanced into Awa. A coup d’état in the sixth month of 1582 resulting in the unexpected death of Nobunaga (an event known as the Honnō Temple Incident) extinguished the pressure from the Oda clan. Having lost the backing of Nobunaga, Yasunaga abandoned the invasion of Shikoku and retreated. This, in turn, provided an opportunity for the Chōsokabe army to resume their operations in Awa.
After recovering Ichinomiya and Ebisuyama castle, Chōsokabe Nobuchika (Motochika’s eldest son) planned to attack Shōzui Castle. Motochika directed his forces to wait until the eighth month, but Nobuchika led a unit as far as Kaifu and, with the support of Kōsokabe Chikayasu, waited for back-up from Motochika. Having considered the weariness of the commanders, the troops, and the local residents, Motochika sent Chikazawa Echigo-no-kami as a messenger and called Nobuchika back to Okō Castle. This was to made adequate preparations in the event of a final showdown with the Miyoshi clan.
At Okō Castle, Motochika held a war council. At this time, he listened in separate rooms to the opinions of the chief retainer and castle lords on one side and those of the armed peasants and jizamurai, or local fighters, on the other. This second group was referred to as the ichiryō-gusoku. The chief retainer and lords raised objections to an offensive, noting the absence of mountains in which to set-up a base, the large number of Miyoshi supporters in Awa, and the fatigue felt after years of conflict. Meanwhile, the representatives of the ichiryō-gusoku argued that unless they opposed them, the Miyoshi would take over not only Awa, but also Tosa. With additional forces from Hashiba Chizuken-no-kami, they should invade Awa to eliminate Sogō Masayasu. Motochika agreed with the representatives of the ichiryō-gusoku, issuing orders for troops to gather for deployment to Awa.
After completing their preparations, the Chōsokabe army visited the Tosa Shrine, donated a scarlet-threaded suit of armor and gold-plated long sword as votive offerings, prayed, and then departed from Okō Castle.
Battle along the Nakatomi River
The Chōsokabe army marched north on the Nankai Road, entered Ushiki Castle, and, after holding a military council, on 8/26, arrived at Ebisuyama and Ichinomiya castles with the aim of proceeding to Shōzui Castle. Prior to their arrival, Masayasu abandoned these castles and concentrated his forces at Shōzui Castle. On 8/27, after gathering all of his troops near the village of Ido, he divided them into three battalions. Chikayasu led 3,000 troops to the southern shores of Nakatomi River. On 8/28, after requesting the opinion of his military strategist, Tōkaku, Motochika issued orders and, around noon that same day, Chikayasu’s battalion at the forward base launched an attack on the northern shore of Nakatomi River.
Shōzui Castle served as the main base to Masayasu’s army. He then set-up a forward operating base at Shōkōji Castle and positioned 2,000 troops near Ōte and 3,000 troops as a rear guard in a defensive posture.
As the battalion led by Chikayasu began to cross the river, the main division of 14,000 forces led by Nobuchika and Chōsokabe Chikayoshi advanced from the southeast, while Chikayasu’s forces came from the southwest so that a total of 17,000 troops attacked from both sides. In addition, having earlier settled with Motochika, Ogasawara Narisuke (the lord of Ichinomiya Castle) and Kuwano Yasuaki (the lord of Kuwano Castle) led 6,000 soldiers to attack the environs of Nakatomi River from the Kuroda Plains. Initially, a counterattack by the Sogō army caused a temporary setback for the Chōsokabe army, but, owing to its size, the attacking forces pressed forward and surrounded Shōzui Castle.
In this battle, almost all of the notable lords of castles associated with the army of Sogō Nasayasu who were active (in the period after the march by Oda Nobunaga upon Kyōto in the ninth month of 1568) were killed in action.
Siege of Shōzui Castle
Riding the momentum of victory in the field battle, Motochika next surrounded Shōzui Castle with 20,000 troops. At this time, reinforcements from the Saika group of Kii Province augmented the Chōsokabe army. Beginning on 9/5, heavy rains continued for the next five days. Behind them, the primary Yoshino River and the Nakatomi River overflowed, causing the Itano Plains to flood and turn into a lake. The Chōsokabe troops were forced to climb on the roofs of homes and into trees to seek refuge. Observing the situation, the Sogō army ventured from the castle in small boats and used long spears to stab the enemy forces from beneath the roofs of the homes and from below the trees. The bird-catcher dance that later became popular in Awa was said to have originated from this battle.
The Chōsokabe army moved their main base to the Kōshō Temple and, after receding of the floodwaters from the Itano Plains, reconstituted their forces and launched another attack. With close combat inside and outside Shōzui Castle, the battle turned into an all-out melee. The chaotic fighting resulted in many dead and wounded on both sides of the battle. In all, a total of 1,503 soldiers were killed, and a significant multiple of this figure were wounded. Commanding the army from his base, Masayasu sought an honorable defeat by preparing to assault the enemy position, but was convinced by a close associate named Higashimura Bingo-no-kami to pull-up and head to Shōzui Castle. Having achieved victory on the battlefield, the Chōsokabe army had a meal in the early evening and them surrounded Shōzui Castle again.
On 9/21, Masayasu vowed surrender to Motochika, and, on the condition that he vacate Shōzui Castle, received a pardon. Masayasu withdrew to Toramaru Castle in Sanuki Province.
After this battle, almost all of the surviving lords of castles in Awa surrendered to the Chōsokabe clan. Among these lords, Motochika suspected Ogasawara Narisuke (the lord of Ichinomiya Castle) and Shingai Dōzen (the lord of Ushiki Castle) of plotting rebellion and had them killed. In the fourth month of 1583, Shinohara Jiton of Kizu Castle incurred an attack by Kōsokabe Chikayasu and fled in defeat to Awaji Province. Mori Muraharu of Tosadomari Castle was the only lord remaining in Awa who continued the resistance to the Chōsokabe clan.