The shogun rode into Edo carrying worse news than anyone in the capital had expected. Tokugawa Hidetada, the second Tokugawa shogun and son of the aging Ieyasu, arrived on March 13, 1615, after months in the west overseeing the aftermath of the Winter Siege of Osaka. He had been there to enforce the peace — a peace that now appeared to be dissolving in real time.

The Winter Siege of 1614 had ended with a truce that looked like a Tokugawa victory. Osaka Castle, the most formidable fortress ever built in Japan, had been systematically stripped of its defenses. Its outer and secondary moats — the features that made the castle nearly impregnable — were to be filled with earth under Tokugawa supervision. In exchange, Toyotomi Hideyori, Hideyoshi's only son and the last symbol of the rival dynasty, would be left alive inside the inner keep. It seemed like a reasonable arrangement. It lasted about two months.

Itakura Katsushige, the Kyoto Shoshidai (京都所司代, Kyōto Shoshidai) — the shogunate's chief intelligence officer in western Japan — had been watching Osaka with growing alarm. His reports to Sunpu and Edo described something that should have been impossible: the filled moats were being excavated again. Hideyori's men were digging them out in plain sight, apparently daring the Tokugawa to object. And the castle itself was filling with men — thousands of them, streaming in from across the country.

They were 浪人 (rōnin) — masterless samurai, men the system had discarded. The word itself carries the image: rō (浪) means wave, and nin (人) means person. A wave person, adrift, with no shore to land on. After Sekigahara in 1600, Tokugawa victory had swept away hundreds of clans, dissolved dozens of domains, and left their samurai retainers without employment, stipends, or purpose. Some had found new lords. Many had not. For fifteen years they had been drifting.

Hideyori gave them a destination. His treasury — the enormous war chest his father Toyotomi Hideyoshi had accumulated as the unifier of Japan — was being opened. Gold and silver, the accumulated wealth of a nation's unification, poured out to buy weapons, repair turrets, and pay the wages of men who had nothing left to sell but their swords. The castle that had been forcibly disarmed was being re-armed with a dead man's ambition.

At Sunpu, seventy-three years old and nominally retired, Tokugawa Ieyasu received the intelligence reports and grasped their implication with the clarity that had kept him alive through six decades of Japanese warfare. His son Hidetada held the formal title of shogun, but every commander in Japan awaited Ieyasu's word. And the word was becoming clear: the winter truce had been insufficient. Hideyori had been allowed to survive, and survival had become a threat.

The rōnin were the critical factor — not merely a military force but a social crisis. These were not hired mercenaries motivated by abstract loyalty to the Toyotomi name; many were men with personal grievances, men ruined by Tokugawa consolidation, men who had watched their lords executed or exiled and their families scattered. Osaka Castle represented, to them, a last chance for something: employment, revenge, the reversal of an order that had disposed of them. The prospect of dying in a great siege was preferable to drifting indefinitely on a peace that had no place for them.

The numbers, recorded in later chronicles, may be exaggerated — the figure of 100,000 rōnin is almost certainly inflated — but the scale was real. Tens of thousands of desperate, skilled, heavily armed men had congregated inside the strongest castle in Japan, under a young lord with the resources to sustain them and every reason to fight. Hidetada's intelligence reports confirmed what the Kyoto governor had been seeing: this was not a garrison. It was an army of the dispossessed, waiting for a siege that everyone now knew was coming.

Within weeks, both Tokugawa commanders mobilized. Ieyasu departed Sunpu on April 4. Hidetada departed Edo on April 10. The armies they assembled — estimates range from 155,000 to 200,000 men — converged on Osaka through the spring roads of central Japan. The Summer Siege began in late May.

The castle fell in June. Hideyori committed suicide in the flames. His mother Yodo-dono died with him. Even his young son was hunted down and executed, leaving no Toyotomi heir to anchor future resistance. The rōnin who had poured into Osaka that spring — men who had ridden one last tide — were extinguished with their employer.

The Sengoku era, the age of warring states that had consumed Japan for a century and a half, was over. The last large mobilization of independent samurai fighting for a cause outside Tokugawa authority had broken against the walls they were hired to defend. After 1615, the rōnin who wandered Japan's roads were a social problem, not a military one. The tide had come in, and gone out, for the final time.