Oda Nobunaga governed with vigour and gradually stabilised the situation in the four lower districts of Owari. But just as he thought he could breathe a little easier, a piece of news from the south stuck in his throat like a fishbone—his father's former beloved general, Yamaguchi Saemonnosuke, stationed at Narumi Castle in Aichi District, had rebelled.
Yamaguchi Saemonnosuke, full name Yamaguchi Noritsugu (historically Noritsugu, but here he is called "Saemonnosuke"), was a veteran general from the time of Oda Nobuhide. Tall and sturdy, with a face the colour of a red date, he wielded a great long hafted spear and was renowned for his bravery on the battlefield. Nobuhide had greatly appreciated him, not only entrusting him with the strategic position of Narumi Castle but often summoning him to discuss important military and political affairs. Narumi Castle lay at the border between Owari and Mikawa, directly facing the power of the Imagawa clan, and its strategic importance was paramount. Yamaguchi Saemonnosuke had defended it for many years, repeatedly repelling Imagawa incursions, and his achievements were many.
Yet every new ruler brings his own men. After Nobuhide's death, Yamaguchi Saemonnosuke became increasingly dissatisfied with the new master of the Oda clan, Oda Nobunaga. He once complained privately to his retainers, "Lord Kazusuke (Nobunaga) is nothing but a brash young man, reckless and without any sense of order. Under his hand, the Oda clan will soon be ruined." Such discontent accumulated day by day. Meanwhile, the Imagawa clan constantly sent envoys to entice him with lavish rewards, and gradually Yamaguchi Saemonnosuke's heart turned away.
Finally, around the 22nd year of Tenbun (1553), Yamaguchi Saemonnosuke made a decision that shook all of Owari—he defected from the Oda and surrendered his castle to Imagawa Yoshimoto.
But that was not all. Yamaguchi Saemonnosuke knew that Oda Nobunaga was not a man to let such a thing pass. With Nobunaga's temper, he would surely raise an army to attack. Therefore, before betraying, he had already made thorough preparations.
Around Narumi Castle, he built two additional fortresses: one to the west called Kasadori Castle, and one to the south called Nakamura Castle. The three fortresses formed a triangle, supporting one another. Yamaguchi himself took command at Nakamura Castle, placed his son Yamaguchi Marujirō in charge of Narumi Castle, and, through Imagawa Yoshimoto's coordination, had the Imagawa retainer Tobe Toyomasa stationed at Kasadori Castle. Tobe Toyomasa, a native of Mikawa, was said to wield a pair of iron maces and was known as "Tobe the Demon" for his ferocity in battle. The three castles were linked by well supplied roads and signal fires, like a spike driven into the southern part of Owari, fixed firmly under Oda Nobunaga's very nose.
When the news reached Kiyosu Castle, Oda Nobunaga flew into a rage.
"That old bastard Yamaguchi!" Nobunaga kicked over the low table in front of him, scattering documents and teacups. "My father treated him well, and yet he dares to betray! Not only does he go over to Imagawa, but he builds castles on my territory? What does he take me for?!"
In his fury, Nobunaga immediately mustered his forces and personally led them against Narumi Castle.
It was a hasty attack. Nobunaga had underestimated the defensive strength of the three castle network. Narumi Castle itself was strong, and with Nakamura and Kasadori responding, the three castles communicated by signal fire and fast horsemen, supporting each other at the slightest sign of trouble. No sooner had Nobunaga's army deployed beneath Narumi Castle than Yamaguchi Saemonnosuke from Nakamura Castle attacked his flank, while Tobe Toyomasa from Kasadori Castle fell upon his rear. Caught between two fronts, Nobunaga fought bitterly for half a day, suffered heavy losses, and finally had to sound the retreat, returning to Kiyosu Castle in disgrace.
This victory made Yamaguchi Saemonnosuke swell with pride. At Nakamura Castle, he held a great feast to reward his troops and sent messengers to Imagawa Yoshimoto with news of the victory, boasting of "a great defeat of the Oda army, with hundreds of heads taken." Imagawa Yoshimoto, overjoyed, lavished him with gold and silver rewards.
From then on, Yamaguchi Saemonnosuke grew ever more arrogant, no longer taking Oda Nobunaga seriously. He began to encroach on Nobunaga's lands, sending troops across the border to plunder villages, steal crops, and even set fire to several hamlets on the edge of Nobunaga's domain. Worse still, he built another castle, Muraki Castle, to the southeast of Narumi, pushing further into the heart of Oda territory.
Nobunaga, in Kiyosu Castle, received each piece of news with a livid face. But this time, instead of exploding in rage, he remained silent for a long while, his fingers tapping dully on the low table, "thump, thump."
His retainers thought he was preparing a massive retaliation and clamoured to be sent into battle. Nobunaga merely waved his hand and said, "Not yet. Let the old fool enjoy himself a few more days."
In the spring of Kōji 1 (1555), Nobunaga finally struck. He did not attack Narumi Castle, nor did he go for Nakamura Castle. Instead, taking advantage of the fact that Muraki Castle had just been completed and its defences were not yet fully stable, he led his elite troops on a night march to surprise it. The garrison of Muraki Castle had assumed that the three castles of Narumi, Nakamura, and Kasadori would block any attack; they never imagined Nobunaga would slip around to strike them directly. Nobunaga's troops descended like heavenly soldiers, breaking through the gates of Muraki Castle before dawn. The captain of the garrison fell in battle, and Nobunaga set fire to the new castle, which had been completed barely a month before.
When word reached Nakamura Castle, Yamaguchi Saemonnosuke stamped with rage. He was about to launch a reprisal when he learned that Nobunaga had already withdrawn to Kiyosu Castle. Although not a large battle, this attack severely dented Yamaguchi's pride and taught him one thing—Oda Nobunaga was by no means the reckless brute he had imagined.
After the loss of Muraki Castle, Nobunaga's next target was Kasadori Castle. If Kasadori fell, Narumi and Nakamura would become isolated outposts and would inevitably fall in time. Nobunaga again marched out, heading straight for Kasadori.
But this time he encountered a hard nut.
The defender of Kasadori Castle, Tobe Toyomasa, truly lived up to his reputation. He was skilled in both martial arts and strategy, commanded his troops with iron discipline, and every one of his men fought fearlessly. Nobunaga's forces launched several fierce assaults, but each time Tobe Toyomasa drove them back. When scaling ladders were raised against the walls, they were smashed by falling logs and stones; when battering rams advanced toward the gate, they were set alight by fire arrows shot from the ramparts. Nobunaga personally led a charge, but Tobe Toyomasa on the castle tower drew his great bow and loosed an arrow that struck the armour plate of Nobunaga's banner bearer, sinking deep into the wood, making everyone break out in a cold sweat.
After several engagements, Nobunaga still could not take Kasadori Castle. The two armies remained locked in stalemate beneath its walls.
Nobunaga returned to Kiyosu Castle, pacing gloomily in the tenshu. He turned the problem over and over in his mind: a direct assault would not work, a siege would take too long, and in any case the enemy at Narumi and Nakamura could stab him in the back at any moment. He needed a way to win without using swords and spears.
After much thought, the corners of his mouth slowly turned up—the smile of a hunter who has just spotted his prey's weak point.
"Someone," Nobunaga called to a trusted retainer and gave him a quiet order. "Go and find out for me: who usually delivers Tobe Toyomasa's letters to Imagawa Yoshimoto? Through whose hands do they pass? What format does he use? What tone? Try to obtain an original letter in his own handwriting."
The retainer departed on his mission. Several days later, an original letter that Tobe Toyomasa had written to one of Imagawa Yoshimoto's administrators was placed on Nobunaga's desk. Although Nobunaga did not like scholarly pursuits, he had excellent handwriting and a sharp eye for calligraphy. He carefully studied Tobe Toyomasa's stroke patterns, his habits of expression, his use of seals. Then he summoned a cultured man skilled at imitating handwriting and, following Tobe Toyomasa's style, composed a forged letter.
The exact content of the letter is unknown to later generations, but its general meaning is not hard to guess. In it, writing as Tobe Toyomasa, the forger secretly "reported" certain ambiguous information to Imagawa Yoshimoto, hinting that Tobe had been in covert contact with Oda Nobunaga, and might even have already agreed to switch allegiance to the Oda at an opportune moment.
The letter was carefully aged, written on the same kind of paper that Tobe used, stamped with an imitation of his seal—so accurate that even the shade of the ink paste was exactly matched. Then Nobunaga had the letter delivered into Imagawa Yoshimoto's hands, through a channel that involved a mid level official in Imagawa's entourage—not one of his most intimate confidants, but someone who had access to important documents. Nobunaga had already bribed this line.
When Imagawa Yoshimoto received the letter, he was in his castle at Sunpu, drinking wine and appreciating flowers with his retainers. He unfolded the paper, read it from beginning to end, and the smile on his face slowly froze.
"Tobe Toyomasa…" Imagawa Yoshimoto murmured the name, his bushy eyebrows gradually knitting into a knot.
The "Number One Archer of the Tōkaidō" was stout of body, pale of face, beardless, and moved with a refined, elegant bearing. He loved to imitate the style of the Kyoto court nobles, powdering his face, blackening his teeth, painting his eyebrows. But do not be deceived by his appearance—Imagawa Yoshimoto was extremely intelligent and deeply suspicious. He had emerged victorious from fierce internal family struggles to seize the position of head of the Imagawa clan, and that was not due to blood alone.
He read the letter over again several times, then called several trusted retainers to a private council. Some noted that the handwriting was indeed extremely similar to Tobe Toyomasa's, and the seal appeared genuine—they did not know that Nobunaga's artisan had already carved an almost identical copy of the seal from the original letter, even mixing the ink paste to the exact shade. Others remarked that Tobe Toyomasa had recently shown some unusual behaviour: after repelling Nobunaga's attacks, he had not pressed the pursuit but had held his castle tightly. That "did not quite accord with his usual manner."
These ambiguous doubts fermented and swelled in Imagawa Yoshimoto's suspicious mind, spreading like mould over his judgment.
A few days later, a command from Imagawa Yoshimoto arrived at Kasadori Castle: "Tobe Toyomasa is to return immediately to Sunpu for important consultations."
Tobe Toyomasa was inspecting the castle walls when the order came. Without overthinking it, he left his deputy in charge, took a few attendants, and rode for Sunpu. After a dusty journey, he finally arrived beneath Sunpu Castle. Before he could even catch his breath, he was led by Imagawa's bodyguards into a side hall.
The hall doors slammed shut behind him. A chill ran through Tobe Toyomasa's heart. He looked around: the hall was empty except for a short sword laid out on a plain white wood tray in the centre.
—That was the form for ordering death by seppuku.
Tobe Toyomasa's face turned deathly pale. He fell to his knees and cried out, "My lord! What crime have I committed? My lord! I have served the Imagawa with utmost loyalty; heaven and earth bear witness!"
No one answered. From outside the hall came a low, stern voice: "Lord Tobe, please take your own life. My lord has granted you the mercy of keeping your head."
Tobe Toyomasa slumped to the floor, his eyes full of disbelief. He had spent his whole life on the battlefield, risking his life for the Imagawa, rendering great service. And now, without even a chance to defend himself, he was being ordered to die for no clear reason. He racked his brains, but could not imagine where he had offended his lord.
The urging came again, more severe than before.
Tobe Toyomasa closed his eyes and sighed deeply. With trembling hands he picked up the short sword, opened his collar, and bared his abdomen. The blade gleamed faintly in the dim lamplight, reflecting a face full of resentment and confusion.
"Oda Nobunaga…" he murmured that name in his final moment. He seemed dimly to understand something, yet also to understand nothing at all.
A flash of the blade.
Blood splattered onto the white wood tray with a dull sound.
When Tobe Toyomasa's corpse was carried out of the side hall, Imagawa Yoshimoto did not even come to look. He merely said casually to an attendant nearby, "Thus shall it be for those who communicate with the enemy."
But the matter did not end there. After putting Tobe Toyomasa to death, Imagawa Yoshimoto, far from feeling reassured, grew even more uneasy. He began to recall the recent activities of Yamaguchi Saemonnosuke and his son—had there been anything suspicious about them?
Since Yamaguchi Saemonnosuke had defected to the Imagawa, although outwardly obedient, might he have secretly maintained contact with Oda Nobunaga? He had never allowed Imagawa troops to garrison Narumi and Nakamura castles, claiming it was "to avoid unsettling the local populace"—was that reasonable? When Muraki Castle was taken by Nobunaga, had Yamaguchi done all he could to relieve it? And as for the person mentioned in Tobe Toyomasa's letter as planning to "coordinate from inside and outside" with the Oda—was Tobe the only one?
These suspicions grew larger and larger in Imagawa Yoshimoto's mind, rolling like a snowball that could not be stopped. He began secretly investigating every move of Yamaguchi Saemonnosuke and his son, while deliberately spreading rumours that "Yamaguchi is secretly in close contact with Oda Nobunaga." When the rumours reached Yamaguchi Saemonnosuke's ears, he was panic stricken. He immediately sent a letter to Sunpu defending himself, writing with great sincerity, even offering to send his son as a hostage to prove his loyalty.
This was a normal course of action to prove one's innocence. But in Imagawa Yoshimoto's view, it was precisely a sign of a guilty conscience.
"If he had not been plotting with the enemy, why would he be so panicked?" Imagawa Yoshimoto sneered to his retainers. "Yamaguchi Saemonnosuke has confessed without being interrogated."
Not long afterwards, a command identical to the one given to Tobe Toyomasa arrived at Nakamura Castle: "Yamaguchi Saemonnosuke and his son Yamaguchi Marujirō are to come to Sunpu together for important discussions."
When Yamaguchi Saemonnosuke received the order, he felt as if he had fallen into an icy pit. Of course he knew how Tobe Toyomasa had died. He also understood that if he went, he would most likely never return. Yet if he refused to go, that would be open defiance, and the Imagawa army would immediately level Nakamura Castle.
He thought through the whole night, and his hair turned mostly grey. In the end, he took his son and set out on the road to Sunpu.
Just before departing, Yamaguchi Saemonnosuke said one thing to his closest retainer, his voice full of desolation and regret: "In my life, I have chosen the wrong master twice. The first time, I should not have betrayed Nobunaga; the second time, I should not have trusted Imagawa. Heaven's will, heaven's will…"
At Sunpu Castle, Imagawa Yoshimoto gave him no chance to defend himself. No sooner had father and son entered the castle gate than they were separated and imprisoned. Soon afterwards, they were both ordered to kill themselves on charges of "communicating with the enemy to commit rebellion."
Before he died, Yamaguchi Saemonnosuke lifted his head to heaven and laughed three times. The laughter was shrill and mournful, echoing through the gardens of Sunpu Castle for a long time. His son Yamaguchi Marujirō, barely twenty years old, was led to the execution ground with tears streaming down his face, weeping inconsolably.
Thus, the lives of father and son were cut short on the cold flagstones of Sunpu Castle.
When the news reached Owari, Oda Nobunaga was practicing swordsmanship in the courtyard of Kiyosu Castle. He listened to the report, tossed his wooden sword aside, and burst into laughter so loud that the leaves in the courtyard shook.
"That fool Imagawa!" Nobunaga slapped his thigh, laughing heartily. "I only sent him a piece of paper, and he killed three of his own generals for me. You could give me ten more such opponents and I would fear nothing!"
His retainers exchanged glances. Some showed delight, others felt a secret shock—Lord Nobunaga's counter plot was both venomous and brilliant. Without expending a single soldier, he had made the enemy tear down their own defences. Three heads had fallen—Yamaguchi Saemonnosuke, Yamaguchi Marujirō, Tobe Toyomasa—and Narumi Castle, Nakamura Castle, and Kasadori Castle were suddenly leaderless. Nobunaga then sent his forces to easily recover all three castles, meeting almost no resistance.
A rebellion that had lasted several years was thus pacified with a single forged letter.
Since inheriting the family enterprise, Oda Nobunaga had fought north and south, endured many ups and downs. He had subdued enemies both inside and outside the clan—Oda Hikogorō, Hayashi Tōkatsu, Shibata Katsuie (who later submitted), Oda Nobuyuki, Oda Nobuhiro, Yamaguchi Saemonnosuke—and his power extended far beyond what his father had achieved at his peak. Shobata Castle, Kiyosu Castle, Iwakura Castle, Furuno Castle, Narumi Castle… one after another they fell into his hands, and banner after banner of "Eiraku Tsūhō" fluttered under the skies of Owari.
Yet he had not yet fully unified Owari Province.
Around his domain still lurked two forces that, for the time being, he could not ignore.
One was the Imagawa clan—controlling Suruga, Tōtōmi, and Mikawa, a vast territory with a powerful army, the greatest daimyō of the Tōkaidō. The head of the Imagawa, Yoshimoto, called the "Number One Archer of the Tōkaidō," possessed both civil and military talents, and his ambition to rule the realm was plain to see. He had gathered around him a host of capable generals and wise ministers, such as Taihō Sessai (though already dead, his influence lingered), Asahina Yasuyuki, Okabe Motonobu, and others, each a seasoned warrior.
The other force was the Ikkō sect of Hongan-ji. The Ikkō faith had a huge following in Owari and Mikawa. The Ikkō formed "Ikkō-ikki," leagues of devotees with terrifying combat power and religious fervour that made even daimyō wary. Within Oda territory were many Ikkō branch temples; their people appeared obedient on the surface, but at any moment they might erupt into revolt, making them a constant thorn in Nobunaga's side.
These two forces stood like high walls blocking Nobunaga's path to "subduing the realm by force."
Let us speak further of the Imagawa.
Imagawa Yoshimoto, son of Imagawa Ujichika, inherited the family in the 5th year of Tenbun (1536). He was short and stout, with a full moon face, graceful in bearing, and loved the way of life of the Kyoto nobility. He often held waka and renga gatherings at Sunpu Castle, summoning court nobles and monks from the capital to lecture on poetry and the classics. He himself could compose waka, play kemari, blow the flute, and even imitated the court nobles by blackening his teeth and painting his eyebrows. Those who did not know him might take him for nothing but a pleasure seeking dilettante.
But those who truly knew him understood that in Imagawa Yoshimoto's belly lay the ambition for the whole realm.
From childhood he had read the Book of Han and the History of the Later Han, and especially admired Duke Huan of Qi's achievement of "honouring the king, expelling the barbarians, convening the feudal lords, and restoring order to the realm." He often said to his retainers, "Duke Huan of Qi could rally the vassals without relying on chariots of war—he used trustworthiness and strategy. If the Imagawa can emulate Duke Huan, taking Kyoto as the centre and issuing commands to the realm, why worry about not achieving the great enterprise?"
To realise this dream, he had long been waiting for the right moment to march west.
Imagawa Yoshimoto possessed superlative diplomatic skills. He understood that to advance west to Kyoto, he must first secure his rear so that no enemy could stab him in the back. To that end, he accomplished two major things.
First, he formed an alliance with the Takeda of Kai. The Takeda of Kai, under Takeda Harunobu (later known as Takeda Shingen), the "Tiger of Kai," were the foremost strategists of the Warring States period. The two clans already had a pact from the time of Takeda Nobutora. To solidify the alliance, Imagawa Yoshimoto married his daughter to Takeda Shingen's eldest son, Takeda Yoshinobu. This political marriage tightly bound the Imagawa of the Tōkaidō with the Takeda of Kai and Shinano. They agreed: the Takeda would expand east, the Imagawa westward, neither invading the other, and supporting each other when necessary.
Second, he made peace with the Hōjō of Sagami. Hōjō Ujiyasu, the hegemon of the Kantō, called the "Lion of Sagami," had long been in conflict with the Imagawa over territorial issues. For decades the two clans had fought back and forth along the border between Suruga and Izu. Imagawa Yoshimoto, gauging the situation, proactively extended an olive branch to Hōjō Ujiyasu, proposing a ceasefire, demarcating the border, and promising mutual non aggression. Hōjō Ujiyasu was busy dealing with Uesugi Kenshin and could not afford to open another front, so he agreed. Thus, the Imagawa and the Hōjō concluded a peace treaty and remained at peace thereafter.
With that, the Imagawa had no further worries to the north, east, or south. They could now concentrate all their forces and push westward—and the first step westward was Mikawa Province.
Mikawa Province lay at the strategic throat of the Tōkaidō. Across the Yamasaki River to the west lay Owari Province and Oda Nobunaga. Mikawa was not large, its land parcelled among many small lords whose relationships were complex. Some supported the Imagawa; some secretly communicated with the Oda; others sided with neither and watched the wind. For Imagawa Yoshimoto to reach Kyoto, he first had to knock down the door of Mikawa, fully incorporate it into his domain, and sweep away all those vacillating minor lords.
Yet Mikawa was not an easy bone to gnaw.
Within Mikawa were the Matsudaira, the Ōgiri, the Fukōzu, the Nishio, and other families. The Matsudaira had a particular connection with Oda Nobunaga—its young lord, Matsudaira Motoyasu (the later Tokugawa Ieyasu), had been a hostage in the Oda household as a child, then later transferred to the Imagawa. At this time he was living as Imagawa Yoshimoto's hostage, confined in Sunpu Castle. This boy would one day become a crucial figure who changed the entire Warring States landscape, but for now he was only a taciturn young man, silently enduring humiliation.
The western part of Mikawa was also full of hidden dragons and crouching tigers. The samurai who served the Matsudaira—Torii Mototada, Ishikawa Kazumasa, Sakai Tadatsugu, and others—though temporarily submissive to Imagawa power, had never forgotten their former lord. They regarded Oda Nobunaga with both hostility and wariness, and they followed Imagawa Yoshimoto with a mixture of obedience and reservation. This complex state of mind made the situation in western Mikawa like a pot of boiling porridge, ready to spill over at any moment.
Imagawa Yoshimoto's westward march would by no means be smooth.
To pacify the outside, one must first bring order to the inside. He had to eliminate the obstinate minor lords in Mikawa, suppress any Ikkō-ikki that might erupt, win over the former retainers of the Matsudaira, integrate the military forces of Mikawa, and only then turn his spear towards his true opponent—the man who sat in Kiyosu Castle in Owari, barely in his twenties yet already showing a sharp edge—Oda Nobunaga.
Imagawa Yoshimoto had ample troops. It was said he planned to mobilise between 25,000 and 40,000 men for his western campaign. Oda Nobunaga could muster no more than three to five thousand. Looking only at the numbers, it should have been a contest with no suspense.
But history has proven again and again that war is never a game of numbers.
In Sunpu Castle, Imagawa Yoshimoto was preparing feverishly for the western expedition. He ordered the making of new battle flags, the forging of new tachi, the conscription of provisions, and the reorganisation of his forces. His gaze passed over the hills of Mikawa, crossed the plains of Owari, and fixed directly on Kyoto—the ancient capital that symbolised the hearts of the realm, a thousand miles away.
And in Kiyosu Castle, Oda Nobunaga also smelled the approach of the storm. He stood at the highest point of the tenshu and looked towards the southeast. Though he could see nothing, he knew that a black wave was slowly rising beyond the horizon, rolling towards him with the force of an avalanche.
Nobunaga was not afraid. On his face, there was even a faint smile—the smile of a hunter who has long awaited his prey and at last hears its footsteps.
The decisive battle that would determine the fate of both the Oda and the Imagawa was now like an arrow on a drawn bowstring, poised to fly.