The gates of Gifu Castle had seen better masters. Oda Nobunaga — warlord, visionary, terror of the age — built this fortress on the crown of Mount Kinka in 1567 and promptly renamed the entire province Gifu in a bid for historical grandeur. From this throne of rock, 329 meters above the Nagara River plain and visible for miles in every direction, Nobunaga declared his motto: 天下布武 (tenka fubu), "unify the realm by military force." The phrase combined 天下 (tenka, "all under heaven") with 武 (bu, "martial power"). He had his seal cut with those four characters. The message was not subtle.

That was 1567. By October 19, 1600, Nobunaga was long dead — cut down at Honnoji Temple in 1582 by his own general, Akechi Mitsuhide. His successor, Toyotomi Hideyoshi, had unified Japan at last — but then Hideyoshi too was dead, in 1598, leaving a five-year-old heir and a power vacuum that had already collapsed into civil war. The dream of 天下 (tenka) had passed through three pairs of hands.

Now Tokugawa Ieyasu, 57 years old, marched through Nobunaga's gates.

Gifu had fallen to the Eastern Army vanguard three weeks earlier, in roughly a single day — an embarrassment for the Western cause. Oda Hidenobu, Nobunaga's own grandson, had been twenty years old and garrisoning a castle his grandfather had made legendary. He held it for one day before surrendering. Ikeda Terumasa talked him out of ritual suicide; he was exiled to the monasteries of Mount Koya. He would be dead by 1605, age 21. The Oda line that had started Japan's unification would not live to see it completed under someone else's name.

On October 19, when Ieyasu entered the castle, its walls were flying Eastern Army banners. Every samurai in that column would have felt the weight of the place — standing where Nobunaga once stood, in the fortress from which the dream of a unified Japan first took shape. Ieyasu was not Nobunaga. He was more patient, more calculating, more willing to wait. But he had waited his entire life for a moment exactly like this one.

While Ieyasu surveyed the castle, news arrived from the northwest: Shimazu Yoshihiro's (Shimazu Yoshihiro's) forces had been beaten back from Sone Castle by Mizuno Katsunari's troops. Not just driven back — the Eastern forces had also razed the outer earthworks of Ogaki Castle itself, Mitsunari's current headquarters. At Ogaki, the news hit like cold water. The Western Army's outlying forces were losing ground, and the great Tokugawa army was now less than 30 kilometers to the east.

The night before, Shimazu Yoshihiro had proposed something audacious: a surprise night attack on the Eastern Army at their camp at Akasaka. With the combined Western forces, the thinking went, a sudden strike in darkness might shatter Ieyasu's command before battle could even be joined. Mitsunari's chief strategist, Shima Sakon — brilliant, proud, and deeply traditional — dismissed the idea as dishonorable. Mitsunari backed him. The Shimazu were legendary warriors, proud to a fault; being refused in those terms, by a man they considered a bureaucrat rather than a soldier, stung deeply. That insult would fester.

With the skirmish lost and Ieyasu in Nobunaga's castle, Mitsunari faced his central problem: Ieyasu might bypass Ogaki entirely and strike directly at Osaka Castle — the seat of the young Toyotomi heir, Hideyori. If Osaka fell, the Western cause was finished. The math was clear: Mitsunari had to get in front of Ieyasu, had to hold the roads west. There was one place where all roads converged, where the mountains funneled movement into a single narrow valley. He ordered the night march.

Ieyasu, meanwhile, received his own intelligence: the Western Army was moving. He ordered his forces to march immediately.

Both armies were heading for the same field. Neither would arrive under torchlight. The decisive battle of Japanese history would begin in fog.