Kato Kiyomasa had earned his reputation in places most samurai never went. He had crossed the sea to Korea in 1592 and 1597 during Hideyoshi's invasions — the Imjin War — and fought hard in brutal campaigns against Korean and Chinese forces. He was 38 years old in 1600, built on a reputation for ferocity and endurance, and famous across Japan for a story that had grown into legend: that he had hunted tigers in the mountains of Joseon. Whether or not the specific incidents were precisely as described, the image fit. Kiyomasa was everything a military man was supposed to be.

Ishida Mitsunari was not. Mitsunari was a bureaucrat — brilliant, efficient, and loyal to the Toyotomi regime in every measurable way, but a man who administered wars rather than fought them. During the Korean campaigns, Mitsunari served as an inspector and reporter, sending assessments back to Hideyoshi in Osaka. Kiyomasa believed those assessments minimized the battlefield accomplishments of the military commanders and elevated Mitsunari's own administrative role. Hideyoshi recalled Kiyomasa from Korea and placed him under house arrest in Fushimi. The humiliation was total.

Fukushima Masanori had his own version of the same wound. At 39, he was Hideyoshi's first cousin — their mothers were sisters — and one of the Seven Spears of Shizugatake, the celebrated warriors who had won the battle that established Hideyoshi's supremacy after Nobunaga's death. He had bled for the Toyotomi family. And now a civilian was using reports and paperwork to define what that blood had been worth.

By 1598, the ikon (ikon) — the deep, festering grudge — had become a plan. Seven generals, Kiyomasa and Fukushima among them, converged on Mitsunari's mansion intending to kill him. Mitsunari fled through a back passage and hid in the residence of a rival lord. Tokugawa Ieyasu personally arranged his safe escort out of Osaka, defusing the crisis with visible magnanimity while privately cataloguing every name that had shown up at that door.

Around August 25, 1600, both men were in motion. Fukushima drove the eastern vanguard toward Gifu and then Sekigahara. Kiyomasa operated separately in Kyushu, besieging the western-held castles of Konishi Yukinaga — opening a second front that stretched western resources and prevented Konishi from returning to the main battle in time. They were fighting Hideyoshi's heir, on behalf of the man who had neutralized the one they actually wanted to destroy. The paradox did not bother them. Mitsunari was going to fall either way, and they would be there when he did.

After Sekigahara, the rewards were proportional to the appetite. Fukushima's domain grew from 200,000 to nearly 500,000 koku (koku). Kiyomasa's expanded from 195,000 to approximately 520,000. They had turned a personal grudge into the largest land grant either of their families had ever held.