The Battle of Inō occurred on 8/24 of Kōji 2 (1556).  Waged between Oda Nobunaga and his younger brother, Oda Nobuyuki (Nobukatsu), this conflict arose from a succession struggle within the powerful Oda Danjō-no-jō family in Owari Province.  This is also known as the Battle of Inōhara.  Inō is located near the Shōnai River in the Kasugai District of Owari.

Prelude to the conflict

Nobunaga and Nobuyuki were sons of Oda Nobuhide of the Oda Danjō-no-jō family.  Nobuhide was a deputy military governor of the four lower districts of Owari.  He originated from the Kiyosu-Oda clan (Oda Yamato-no-kami family), serving as a senior retainer and member of one of three designated families serving the Kiyosu-Oda clan.  Known as the Three Commissioners of Kiyosu, these families included the Inaba-no-kami family, the Tōzaemon family, and the Danjō-no-jō family.  In addition to internal conflicts, the Oda clashed with clans in neighboring provinces, including the Matsudaira clan of Mikawa, the Imagawa clan of Suruga, and the Saitō of Mino.  In one generation, the Danjō-no-jō family expanded their influence within Owari and beyond.  After the sudden demise of Nobuhide in 1551, Nobunaga, as the eldest son and lord of Nagoya Castle, succeeded his father.  Meanwhile, during the latter years of Nobuhide’s life, Nobunaga’s younger brother of the same mother, Nobuyuki, separated from Nobunaga and resided in Suemori Castle.

In 1555, Nobunaga leveraged the authority of the Shiba clan (the military governors of Owari) to eliminate Oda Nobutomo, the deputy military governor of the four southern districts of Owari from the main branch known as Kiyosu-Oda clan, and moved to Kiyosu Castle, the base for the military governor of Owari from where he steadily increased the stature of the clan left by his father.  However, Nobunaga had ordinarily been known to demonstrate improper behavior, even being cast as a fool.  Moreover, in 1553, Hirate Masahide, who had been appointed to raise and educate Nobunaga, killed himself.  Within the family, Nobunaga was not viewed as appropriate to serve as its leader.

On top of these circumstances, Yamaguchi Noritsugu, the lord of Narumi Castle, a stronghold on the provincial border with Mikawa, rebelled and switched allegiance to the Imagawa clan.  In 1556, a political incident occurred in Mino by which Saitō Yoshitatsu, the eldest son of Saitō Dōsan (the father-in-law and patron of Nobunaga), killed Dōsan in battle.  Nobunaga also came into conflict with the Iwakura-Oda clan (Oda Ise-no-kami family), the deputy military governors of the four upper districts in Owari and counterpart of the Kiyosu-Oda clan, who were allied with Yoshitatsu.  Consequently, Nobunaga faced ongoing challenges to his position.

In the midst of these conditions, clan elders including Hayashi Hidesada, Hayashi Mimasaka-no-kami (Hidesada’s younger brother also known as Michitomo), and an elder retainer of Nobuyuki named Shibata Katsuie, regarded Nobunaga as incapable of leading the Oda Danjō-no-jō family so they expelled him and arranged for Nobuyuki to become the successor to Nobuhide.  Meanwhile, Nobuyuki himself adopted the multi-generational name of Danjō-no-jō and seized the territory including Shinoki that had been under the direct control of Nobunaga, built a fortress, and demonstrated his intent to resist.

After learning of these unsettling developments, on 8/22, Nobunaga ordered Sakuma Morishige to construct a fortress in Nazuka.  On 8/24, this escalated into a battle at Inōhara.

The Battle of Inō

As Nobunaga’s army crossed the Otai River to the southeast of Kiyosu, a battle arose as the Shibata army approached from the east and the Hayashi army from the south.  Nobunaga led less than 700 soldiers (including Sakuma Morishige, Mori Yoshinari, Sakuma Nobumori, Maeda Toshiie, Niwa Nagahide, and Oda Nobufusa) against a combined army of 1,700 men (1,000 forces led by Shibata Katsuie and 700 forces led by Hayashi Hidesada) backing Nobuyuki.  Around noon, about one-half of Nobunaga’s army attacked the Shibata forces, but owing to the numerical inferiority, in addition to the battle tactics of Katsuie, senior retainers of Nobunaga including Sassa Magosuke (the elder brother of Sassa Narimasa and one of the Seven Spears of Komakizaka) were killed in succession, placing Nobunaga in a precarious situation.  When the Shibata army approached Nobunaga’s main base, only forty soldiers with spears including Oda Shōsaemon, Oda Nobufusa, and Mori Yoshinari stood between him and the enemy forces.

However, Oda Nobufusa and Mori Yoshinari fought valiantly on the front lines of the battle, killing an opposing bushō named Tsuchida-no-Ōhara from the Kiyosu group.  At that time, when Nobunaga screamed at the enemy, members of the Shibata army were said to have fled in the midst of a battle between members of related families.  According to the diary of a Jesuit missionary named Luís Fróis residing in Japan during this period, Nobunaga possessed an unusually loud voice.  Having reclaimed momentum, Nobunaga’s army attacked the Hayashi forces.  During the battle, when Mimasaka-no-kami became entangled with Kuroda Hanpei and could not breathe, Nobunaga thrust his spear and killed the enemy.  In total, the combined army backing Nobuyuki lost over 450 soldiers, including Kamata Suke-no-jō, Tomino Sakyō-no-shin, Yamaguchi Matajirō, Hashimoto Jūzō, Ōwaki Torazō, and Kanbe Heishirō.

In the end, the forces fighting for Nobuyuki collapsed and fled in defeat.  Thereafter, supporters of Nobuyuki holed-up in Suemori and Nagoya castles.  Nobunaga responded by burning down the towns below these castles.

Aftermath of the battle

After the defeat of Nobuyuki, Dota Gozen, the natural mother of Nobunaga and Nobuyuki, interceded to spare the life of Nobuyuki. Nobukatsu met Nobunaga at Kiyosu Castle and was forgiven.  Moreover, senior commanders who fought for Nobuyuki including Hayashi Hidesada, Shibata Katsuie, and Tsuzuki Kurando apologized and pledged their loyalty to Nobunaga.

Later, Nobuyuki plotted another rebellion, but was deceived by the elder Katsuie who had already abandoned Nobuyuki in favor of Nobunaga. On 11/2 of 1557, upon hearing that Nobunaga was ill, Nobukatsu paid a visit to Kiyosu Castle whereupon he was assassinated by Kawajiri Hidetaka and others between the north watchtower and the secondary keep upon orders of Nobunaga.

Over twenty years later, in 1580, Hidesada was ousted by Nobunaga.  Among the reasons given by Nobunaga for this action was that Hidesada fought against him at the Battle of Inō.