In January 1610, the harbor at Nagasaki became a war zone. Arima Harunobu, the Christian daimyō (feudal lord) of Hizen, had arrived with 1,200 armed samurai. His target was a single Portuguese trading vessel: the Nossa Senhora da Graça — known to the Japanese as a kurofune (black ship) — commanded by Captain-Major André Pessoa. What followed was a four-day naval siege that ended with the ship exploding in a pillar of fire.

The backstory was personal. In 1608, Japanese sailors from Harunobu's trading ship had been wintering in the Portuguese colony of Macao after a voyage to Cambodia. The crew behaved badly — walking through town in armed bands of thirty or forty, alarming the Chinese inhabitants. When the Portuguese authorities tried to restrain them, a serious brawl broke out. Pessoa, who held military authority in Macao, suppressed the riot by force, killing roughly forty Japanese crewmen and imprisoning around fifty others.

When survivors returned to Japan in September 1609 and told their version of events, Harunobu was furious. He petitioned Tokugawa Ieyasu for permission to take revenge. Ieyasu hesitated — attacking a Portuguese ship could endanger the lucrative annual trade between Nagasaki and Macao. But fate intervened: a Spanish ship sailing from Manila to Mexico was wrecked off eastern Japan around the same time, and the political calculations shifted. Ieyasu gave the order.

Harunobu first tried to lure Pessoa ashore with offers of hospitality, claiming he only wanted to negotiate silk prices and that Pessoa would be pardoned even if found guilty. But Pessoa — tipped off through the Christian community in Nagasaki — wasn't fooled. He knew Harunobu had assembled a force of 1,200 men. He refused to leave the ship even for Mass, stockpiled grenades and ammunition, and ordered his full crew aboard to prepare for departure.

But the cargo was enormous, and the ship wasn't ready to sail by New Year's. Previous Portuguese vessels usually departed before Christmas. Pessoa had waited too long.

The attack began on January 3. Harunobu's samurai approached in war junks, attempting to board the massive carrack. Pessoa's crew — roughly forty Europeans manning some forty cannons, along with auxiliary fighters — drove them back with artillery fire, sinking or scattering several attacking vessels. For three days, the pattern repeated: assaults, repulsions, brief negotiations that went nowhere. During one exchange, Pessoa demanded the sons of both Harunobu and another local official as hostages. Harunobu didn't reply. Instead, word came from the shogunate's local representative that Harunobu had direct orders to kill Pessoa.

On the morning of January 6, a favorable breeze finally allowed Pessoa to move the ship toward the neighboring anchorage of Fukuda. Seeing his prize about to escape, Harunobu gave chase in a flotilla led by a colossal tower-junk. This time, samurai managed to board the carrack.

What happened next stunned everyone watching from shore. Rather than surrender the vessel and its cargo — Chinese silk, porcelain, and Southeast Asian goods — Pessoa ordered the powder magazine lit. The Nossa Senhora da Graça erupted in a catastrophic explosion, taking Pessoa, his crew, and everything aboard to the bottom of Nagasaki harbor. The few Portuguese who survived the blast and swam ashore were seized and beheaded.

Pessoa's desperate act of defiance impressed the Japanese, and memories of it persisted well into the 19th century. But its consequences were lasting. Ieyasu rewarded Harunobu with a prized sword and a marriage alliance for his son — but the incident confirmed Portuguese traders as troublesome in Tokugawa eyes. The shogunate began tilting toward the Dutch. Within three decades, Portugal would be expelled from Japan entirely, and the country would seal itself shut for over two centuries.