The ink was barely dry when Ii Naosuke knew the knives were being sharpened. On July 29, 1858, the 大老 (tairō) — the Tokugawa shogunate's most powerful official — put his seal to the Treaty of Amity and Commerce aboard the USS Powhatan riding at anchor in Edo Bay. Five ports would open to American trade: Kanagawa, Nagasaki, Niigata, Hyogo, Edo. American citizens would be exempt from Japanese law. A fixed tariff schedule would strip the shogunate of its ability to protect Japanese industries. Two centuries of 鎖国 (sakoku) — the closed-country policy that had defined Japan's identity — were finished.

But no one had asked the Emperor.

In Kyoto, Emperor Kōmei had explicitly refused to sanction any such agreement. This was unprecedented. For generations, the Emperor had been a ceremonial figure, rubber-stamping shogunate decisions. Now, for the first time, the Son of Heaven told the bakufu no — and the bakufu had proceeded anyway. The rupture between imperial court and military government, papered over for centuries, cracked open.

Ii Naosuke was 42 years old when he signed. He was the 14th son of the lord of Hikone — a man who had spent his youth as a ward in a Buddhist temple, with no expectation of ever holding power, writing poetry and practicing tea ceremony in resigned obscurity. Thirteen elder brothers died or were adopted away. He inherited by accident, rose by ability, and became Tairō in April 1858 because the shogunate was in crisis and needed someone willing to act.

His calculation was brutally rational. Townsend Harris, the American consul who had waited two years at the temple of Gyokusen-ji in Shimoda, refused proper diplomatic facilities, slowly wearing down Japanese resistance through sheer patience, had made one thing clear: British and French fleets were en route to Japan, fresh from forcing the Qing dynasty to its knees in China. Those powers would extract far worse terms at cannon-point. Harris's treaty, Ii decided, was the lesser catastrophe.

He signed. Within weeks, nearly identical treaties followed with the Netherlands, Russia, Britain, and France — the Ansei Treaties 安政条約 (Ansei Jōyaku), what later Japanese historians would call the "unequal treaties" 不平等条約 (fubyōdō jōyaku) because they granted Western nations privileges Japan could never reciprocate. The demand to revise them would drive Japanese foreign policy for the next four decades.

Ii's response to the political firestorm was the Ansei Purge 安政の大獄 (Ansei no Taigoku): more than 100 opponents — court nobles who had lobbied against the treaties, scholars who published criticism, rival daimyō who had defied the shogunate — were arrested, exiled, or executed. It was the most aggressive government crackdown in generations. It silenced the loudest voices. It also created martyrs.

On March 24, 1860, Ii's palanquin left Edo Castle through the Sakurada Gate. Seventeen rōnin from Mito domain — the most ardent imperial loyalist domain in Japan — had been waiting in the snow. They killed his guards, dragged him from his palanquin, and cut off his head. The shogunate refused to confirm his death for a full month, claiming he was merely "recuperating." The fiction convinced no one. The Tokugawa's prestige never recovered. Eight years later, the Meiji Restoration ended 265 years of shogunate rule.

Ii Naosuke bought Japan time. He paid for it himself.