Battle of Aga
Date: Fifth month of Tenshō 5 (1577)
Location: Aga in Harima Province
Synopsis: Aiming for Himeji, Nomi Munekatsu sailed with 5,000 troops from the Kobayakawa navy to Aga on the coast of Harima, intent on securing a key base for the Mōri. Knowing the enemy sailors would, upon landing, be weary from their long journey at sea, the Kodera planned a surprise attack before the invaders could recover. Meanwhile, Kuroda Yoshitaka had local residents display war banners, deceiving the sailors into believing the Kodera were backed by reinforcements and causing them to retreat.
The Battle of Aga occurred in the fifth month of Tenshō 5 (1577) at Aga in Harima Province. This conflict was waged between Nomi Munekatsu (Ura Munekatsu), a commander of the naval forces of Kobayakawa Takakage, and Kodera Masamoto, the head of the Kodera who submitted to Oda Nobunaga. Aiming for Himeji, Munekatsu landed in Aga in the territory of Miki Michiaki of Harima who was allied with the Mōri clan.
At this time, Harima was in-between the spheres of influence of the Oda (Oda Nobunaga) from the east and the Mōri (Mōri Terumoto) from the west, causing tensions among those in the province to decide which side to choose. The 5,000 troops sent by the Mōri were ten times the number of men on the side of the Kodera but based on the brilliant tactics of Kodera Yoshitaka (Kanbei, later known as Kuroda Yoshitaka), the defenders repelled the Mōri army.
Marching east to Harima, from the fourth to fifth months of 1575, the Mōri advanced their forces toward Himeji with Kōzuki Castle serving on the front lines. In the fourth month, the forces landed in Murotsu and, from Aga, aimed to march to Himeji. Aga was a central location for ikkō monks in Harima and the Mōri set-up a military base in this same area. During this time, Kobayakawa Takakage advanced to Bitchū-Kasaoka and built their main base. His nephew, Mōri Terumoto (the head of the Mōri), established a base at Mihara in Aki Province.
Aga was in the territory controlled by Miki Michiaki. A retainer named Miki Seikan was the husband of his younger sister so initially he was cooperative with Takakage such as by rushing to assist at the Battle of Aoyama-Kawarakeyama. Therefore, he had a close relationship with the Kodera. In Michiaki’s territory, however, at the Aga monastery, there were many ikkō monks affiliated with the Hongan Temple and Michiaki himself was an ardent follower of the faith. In 1570, after the start of the Ishiyama War, Michiaki acted in concert with calls from Kennyo (the eleventh high priest of the Hongan Temple) and rebelled, providing support by sending 430 troops to the Kinai and 3,000 hyō of rice to the Ishiyama-Hongan Temple, making clear his opposition to the Oda. This caused alienation from other powers aligned with the Oda, beginning with Kodera Yoshitaka (the strongest support of the Oda in Harima) along with those who leaned in favor of the Oda including the Akamatsu clan (Akamatsu Norifusa and Akamatsu Hirohide), the Kodera clan (Kodera Masamoto), and the Bessho clan.
In 1576, based on the decision by Mōri Terumoto to support the Hongan Temple, the two parties had a mutual enemy in Oda Nobunaga so Michiaki allied with the Mōri and cooperated by allowing the Kobayakawa navy (Munekatsu’s forces) dispatched by the Mōri to land in his territory.
Course of events
The Kodera fielded a total of 2,000 troops but had to allocate a majority of these troops to support Masamoto in the defense of Gochaku Castle and to the Kuroda clan at Himejisan Castle. Yoshitaka had only 500 troops remaining in his command to form the Kuroda army. Meanwhile, the Mōri sent 5,000 troops. A head-on clash would not yield a victory so Yoshitaka devised a strategy.
Given that their opponents were sailors, Yoshitaka knew that after coming ashore, they would be in a tired and vulnerable state after being on the ocean for an extended period, so he took this recovery period as an opportunity to launch a surprise attack. He also called out to local residents (peasants) to have them display war banners. Munekatsu, who was a prominent commander within the Mōri family, attempted to recover, but believing that the banners raised by the peasants were from a reinforcement army, the Mōri decided to withdraw and pull back to Kōzuki.
After defeating an army with ten times as many troops, this remarkable feat by Kodera Yoshitaka served as a catalyst for the fortune of his family and provided an opportunity for Nobunaga to attack the Mōri. Before long, Nobunaga appointed Hashiba Hideyoshi as the commander-in-chief for the Invasion of Chūgoku.
In the tenth month of 1577, after the Hashiba army entered Harima, Yoshitaka presented Himejisan Castle to Hideyoshi who then made the castle his main base for battles across Harima and Tajima provinces. During the invasion, Yoshitaka was relied upon heavily by Hideyoshi. Later, Yoshitaka (under the name of Kuroda Kanbei or Kuroda Yoshitaka) served as a military strategist for Hideyoshi on a par with Takenaka Shigeharu (Hanbei).