Kiyosu Castle rose at the intersection of two of Japan's most important medieval highways. The Ise Kaido connected the great shrines of Ise with the interior, while the Nakasendo ran through the mountainous center of Honshu between Kyoto and Kamakura. Whoever controlled this junction controlled the flow of trade, troops, and information across Owari Province. The castle was commissioned under the authority of Shiba Yoshishige, head of the Shiba clan and governor of Owari, Echizen, and Totomi Provinces. Upon completion, Oda Toshisada was installed as vice-governor, making the castle the operational center of Oda influence in the region. Initially, Kiyosu served as a defensive outpost protecting Orizu Castle, the actual seat of provincial government. But when Orizu was destroyed in 1478 during a civil war between rival Oda factions, Kiyosu absorbed its political functions and became the center of power in lower Owari.

The Oda clan's internal politics were merciless, and Kiyosu Castle witnessed the worst of them. After Oda Nobuhide died in 1551, his son Nobunaga -- young, eccentric, and widely underestimated -- struggled to consolidate control. Nobuhide's younger brother Oda Nobutomo, backed by Shiba Yoshimune, seized Kiyosu Castle in 1553. The power play backfired spectacularly. In 1554, Yoshimune revealed an assassination plot against Nobunaga. Nobutomo responded by having Yoshimune killed. The next year, Nobunaga struck. He retook Kiyosu Castle by force, captured his uncle, and compelled him to commit suicide. The castle's violence was not finished. In 1557, Nobunaga had his own younger brother, Oda Nobuyuki, assassinated inside Kiyosu Castle's donjon -- the tower that was supposed to represent the family's strength. By the time Nobunaga invited Tokugawa Ieyasu to Kiyosu for treaty negotiations in 1562, the castle's walls had absorbed more Oda blood than enemy blood.

The Nobunaga-Ieyasu alliance forged at Kiyosu Castle in 1562 was one of the most consequential diplomatic acts of the Sengoku period. The two warlords agreed to a pact that would endure for decades, with Ieyasu controlling the eastern flank while Nobunaga pushed westward toward Kyoto and national dominance. It was a partnership born of pragmatism -- each man needed the other's strength -- but it held, outlasting most alliances of the era. Nobunaga relocated from Kiyosu to Iwakura Castle in 1563, leaving behind the fortress that had made him. After Nobunaga's assassination in 1582, Toyotomi Hideyoshi gathered the late warlord's retainers at Kiyosu Castle and proclaimed his regency over Nobunaga's infant grandson, Oda Hidenobu. The castle passed to Nobunaga's second son, Oda Nobukatsu, who launched major renovations in 1586, adding a double ring of moats and both a large and small donjon.

The original Kiyosu Castle did not survive the centuries. Like many Japanese castles, it was dismantled, its materials repurposed, its moats filled. What stands today on the banks of the Gojo River is a modern reconstruction, built as a centennial celebration for the city of Kiyosu. A bronze statue of Oda Nobunaga stands in the adjacent park, gazing out with the fierce composure of a man who murdered his way to the top and then remade a nation. Cherry trees line the riverbank, and in spring, the castle's white walls and curved rooflines rise above clouds of pink sakura blossoms -- a scene of profound tranquility at a site whose history is anything but tranquil. The reconstruction serves as a museum and cultural center, preserving the memory of the castle's role in the pivotal decades when Japan's warring provinces were hammered into a unified state. The original stone walls remain partially visible, a reminder that beneath the cherry blossoms and the tourist signage lies a place where ambition, betrayal, and genius converged.