It began with a pregnant woman in a river.

The tax collector of 島原 (Shimabara) Domain — serving the 大名 (daimyō) 松倉勝家 (Matsukura Katsuie), a man who had spent years wringing impossible levies from an already exhausted peasantry while also enforcing the Tokugawa ban on Christianity with particular brutality — had run out of patience with a village chief who could not meet his tax obligations. His solution was to arrest the man's daughter-in-law, place her in a wicker basket, and submerge her in the icy waters of a river in late November. She drowned in the cold. Her father-in-law and her father rose with approximately 700 farmers and burned the collector's house to the ground.

The fire spread. Across the 島原半島 (Shimabara Hantō) — the Shimabara Peninsula — and the 天草 (Amakusa) islands, a generation of peasants who had endured crushing taxation, violent repression, and the death penalty for practicing the faith their grandparents had received from Portuguese missionaries rose together. And into this rising, in the last days of November 1637, a boy was proclaimed.

益田四郎時貞 (Masuda Shiro Tokisada) — known to history as 天草四郎 (Amakusa Shiro) — was approximately fifteen or sixteen years old. He had grown up on 天草 (Amakusa) island, in the Amakusa archipelago of Higo Province (present-day Kumamoto Prefecture). His father, 益田甚兵衛吉次 (Masuda Jinbei Yoshitsugu), had been a samurai retainer of the Christian 大名 (daimyō) 小西行長 (Konishi Yukinaga) — baptized "Augustine Konishi" — who was executed after the Battle of 関ヶ原 (Sekigahara) in 1600 for his faith and his allegiance to the losing Western coalition. The family had survived his disgrace by relocating to the islands, maintaining their Christianity in secret, raising their son in a faith that was simultaneously their heritage and a capital crime.

Shiro had reportedly received education in 長崎 (Nagasaki), possibly through the covert networks left by Jesuit missionaries. He could read. He carried himself with a quality that observers — then and in the accounts that followed — described as something between gravity and light. He was the son of a samurai, which gave him warrior credibility among the 浪人 (rōnin) in the uprising. He was a Christian of apparent depth and charisma, which gave him spiritual authority among the peasants. And he was young enough that the miracles people projected onto him encountered no skeptical resistance from a life already explained.

The miracle stories circulated and were embellished. One famous account: while Shiro prayed, a dove descended from the winter sky and laid an egg in his outstretched hands. When he cracked the egg open, inside was a tiny image of Christ and a scroll of scripture. The dove cried "zuiso" — understood to mean "Jesus" — three times and flew away. Another account held he had walked on water. Another, that he had restored sight to a blind girl. These stories blended Jesuit Christian hagiography with the supernatural expectations of the Japanese warrior tradition, and they spread the way stories spread when people are frightened and need to believe something.

37,000 people eventually gathered with him — rebels and their families, farmers and former samurai and 切支丹 (Kirishitan) practitioners who had kept the faith for three decades underground — at the ruins of 原城 (Hara-jō) on the Shimabara Peninsula. The castle had been demolished by the Tokugawa some years before, but its stone walls still stood. They provisioned it as best they could and they waited.

The Tokugawa shogunate's response was, in scale, extraordinary. Over 125,000 troops were eventually mobilized to surround the castle. In a detail that captures the surreal geometry of this moment in history, the Dutch East India Company (VOC) — Protestant traders who had no objection to helping the Tokugawa suppress Japanese Catholics — provided a warship that bombarded 原城 (Hara-jō) from the sea. Protestant Europe and the Tokugawa Shogunate, working in concert against a castle full of Japanese Catholics praying to a teenage messiah.

The castle fell on April 12, 1638, after approximately three months of siege. 天草四郎 (Amakusa Shiro) was beheaded. Approximately 37,000 people — men, women, children — were killed. His severed head was taken to 長崎 (Nagasaki) and displayed on a pike in the harbor — the same harbor where Portuguese missionaries had first landed a century before, where the faith he had died for had first arrived in Japan.

He was sixteen years old, or thereabouts. No one had recorded the date precisely enough to be certain.