There is a phrase that every child in Aizu domain learned before they learned much else: ならぬことはならぬものです (Naranu koto wa naranu mono desu). It comes from the 什の掟 (Jū no Okite), the moral code written for the children of Aizu's samurai families. The translation is simple: what must not be done, must not be done. No reasoning, no exception, no negotiation. Some things are simply prohibited, and the prohibition is itself the answer.

By mid-October 1868, the Aizu were living entirely inside that phrase.

鶴ヶ城 (Tsurugajō, Tsuruga Castle) in Aizuwakamatsu had been under siege since October 6. Inside the walls: approximately 5,000 people — samurai, their families, the wounded, the elderly, children. The 戊辰戦争 (Boshin Sensō, Boshin War) had already swept through most of Japan. The Tokugawa shogunate had been overthrown. Domain after domain had submitted to the new Meiji imperial government. Aizu alone had not.

It could not. The domain's founding code — laid down by Hoshina Masayuki (保科正之), the ancestor who established the Aizu branch of the Matsudaira (松平) family — contained Article 1 as an absolute: be faithful to the Tokugawa shogun. This article existed not as a preference or a guideline but as the moral foundation on which Aizu's identity rested. The domain had been the Tokugawa's most trusted defender. When the shogunate was gone, the Aizu had no framework for what they were supposed to be instead.

The castle's defenders knew the military situation. The imperial coalition outside had fifty cannons. Over a thousand shells per day struck the castle or its grounds on average — on October 29, fifty cannons each fired fifty shells, a single day's total of 2,500 impacts. The stone walls were repaired continuously under fire. Every room held wounded men. Roof tiles were stripped from above the defenders' own heads and melted down for buckshot. Women hauled water through the bombardment. The castle's food stores were declining with no possibility of resupply.

The tragedy above the castle had already happened. The 白虎隊 (Byakkotai, White Tiger Corps) — teenage boys, ages fourteen to seventeen, assigned to defend the castle's perimeter — had become separated from the main garrison on October 8. From the hill of 飯盛山 (Iimoriyama), they had seen smoke rising from the direction of the castle and concluded it had fallen. Nineteen of them committed 切腹 (seppuku, ritual suicide) on that hillside rather than survive what they believed was Aizu's end. The castle had not fallen. The smoke was from the burning town. Eighteen died. One — fourteen-year-old Iinuma Sadakichi (飯沼貞吉), who had lied about his age to join — survived with his wounds. He lived until 1931.

Inside the castle, Matsudaira Katamori (松平容保), lord of Aizu, age 32, held command. He had spent six years as Kyoto Shugoshoku (京都守護職) — Military Commissioner of Kyoto — and in that role had founded and patronized the 新選組 (Shinsengumi), the shogunate's elite Kyoto police force. He had been the Tokugawa's most visible enforcer during the final years of the regime. When the regime fell, he was the most obvious target of imperial anger — and he knew it.

He stayed inside the castle.

Also inside, at age 8: Sutematsu (捨松), daughter of an Aizu retainer, who would survive the siege, survive the prison camp that followed, survive the exile, eventually be sent to America for education, graduate from Vassar College magna cum laude in 1882 as Japan's first female college graduate, return to Japan, and marry the Meiji government's own Minister of War. She spent her childhood in this castle under cannon fire and her adult life in the world that besieged it. History did not give her a straightforward narrative.

The castle held. Day by day, October into November. The code said it must. The men and women inside obeyed the code.

On November 6, 1868, Aizu finally surrendered — unconditionally, mediated by Yonezawa Domain. Katamori presented himself in person before the imperial commanders. The surviving samurai were marched to prison camps. The civilians — roughly 17,000 survivors — were exiled to the 斗南藩 (Tonami han) on the Shimokita Peninsula in northern Aomori: a barren, cold stretch of land where farming was nearly impossible. Many of the elderly and children did not survive the first winter.

The punishment extended to language. The Meiji government erased the name 'Aizu' from official maps, renaming the territory 'Wakamatsu Prefecture.' A domain that had held a castle under two thousand cannon shots a day for a month was not even allowed to keep its name.

Katamori himself was placed under house arrest, lived in poverty for years, and in 1880 was appointed head priest of 日光東照宮 (Nikkō Tōshōgū) — the shrine to the deified Tokugawa Ieyasu, the god Katamori had nearly died protecting. He served as priest until his death in 1893. Whether the appointment was mercy or the Meiji government's version of a joke, no one explained at the time.