The castle had a name that sounded like an omen: 鶴ヶ城 (Tsurugajō), Crane Castle. Before the war, its white plastered walls rising above Aizu's mountain basin had given it the look of a great bird with wings spread — elegant, motionless, enduring. In October 1868, those walls were about to be tested by something the samurai who built them had never imagined: modern Western artillery, fired day after day, sometimes a thousand shells in a single afternoon.

By October 1868, the Boshin War (戊辰戦争, Boshin Sensō) had already been largely decided. Edo — the shogunal capital — had fallen to the imperial forces in the spring without the bloodbath everyone expected. The last Tokugawa shogun, Yoshinobu (徳川慶喜, Tokugawa Yoshinobu), had stepped down. Domain after domain had submitted to the new Meiji government. In the southwest, the great reforming domains of Satsuma and Chōshū (薩摩 and 長州, Satsuma and Chōshū) that had driven the revolution now administered the new order.

Aizu (会津) had not submitted. It would not.

The Aizu domain — the 会津藩 (Aizu-han) — had been among the most fiercely loyal to the Tokugawa for over two centuries. Its lord, Matsudaira Katamori (松平容保, Matsudaira Katamori), born September 5, 1836, was 32 years old in 1868. From 1862 to 1868 he had served as the Tokugawa shogunate's 京都守護職 (Kyoto Shugoshoku) — Military Governor of Kyoto — the man charged with maintaining order in the imperial capital on behalf of the shogunate. In that role he had deployed and overseen the 新選組 (Shinsengumi), the notorious special police corps that hunted down anti-shogunate activists with a ruthlessness that made Aizu hated across the southwest. The new government had not forgotten.

For this loyalty, Aizu would pay.

On the morning of October 6, 1868, the final battle for the approaches to Aizu was fought at Bonari Pass (母成峠, Bonari-tōge). Itagaki Taisuke's (板垣退助, Itagaki Taisuke's) imperial force of roughly 3,000 men — equipped with modern rifles and superior numbers — struck the defending rearguard of approximately 800 men: a combined force of former Tokugawa troops and Aizu soldiers that included a detachment of the Shinsengumi under Hijikata Toshizō (土方歳三, Hijikata Toshizō). The pass fell. Hijikata and the surviving remnants retreated northward toward Sendai and eventually Hokkaido, where Hijikata would make his final stand and die in 1869. Aizu's last outside allies were gone.

That afternoon, imperial forces completed their encirclement of Tsurugajō. The siege had begun.

Inside the castle walls, approximately 5,000 people were now sealed in — not just samurai fighters, but women, children, the elderly, and the wounded. Most of Aizu's mobile fighting forces had been deployed in the field throughout the summer campaign and were now cut off, destroyed, or scattered. The castle garrison was reduced. But Matsudaira Katamori and those who remained refused to surrender.

Among those fighting outside the castle walls before the encirclement was complete was Nakano Takeko (中野竹子, Nakano Takeko), born April 1847, age 21. A highly skilled practitioner of 長刀 (naginata) — the curved-blade polearm associated with female martial training — she had organized an unofficial women's unit, the 娘子軍 (Jōshigun), with roughly 20 to 30 women and fought alongside the Aizu forces in the surrounding battles. On October 16, 1868, she was fatally shot in the chest during a charge. As she lay dying, she asked her younger sister Yūko (竹子の妹 結子, Yūko) to behead her — a deliberate act to deny the imperial troops the satisfaction of taking her head as a war trophy. Yūko did so. Nakano Takeko's head was buried at Hokai Temple, where it remains today.

Also fighting for Aizu — and suffering one of the war's most haunting episodes — were the 白虎隊 (Byakkotai), the White Tiger Unit: 16- and 17-year-old sons of Aizu samurai families, formed in April 1868 as a reserve force when it became clear that every able-bodied fighter would be needed. Following fighting near the castle town, a small sub-unit of roughly 20 boys became separated from the main force and climbed 飯盛山 (Iimoriyama), Mt. Iimori, overlooking the city. From there they saw smoke rising from the burning town below and, believing Tsuruga Castle had already fallen, concluded that all was lost.

They committed 切腹 (seppuku) together on the hillside.

The castle had not fallen. The smoke was from houses burning in the castle town — the keep itself still stood. Of the boys on Iimori Hill, one survived: Iinuma Sadakichi (飯沼貞吉, Iinuma Sadakichi), who had failed to die and was eventually found and helped by a passing villager. He lived to old age. He outlived the world those boys had died for.

The imperial artillery opened its heaviest bombardment on October 29. Fifty cannons, each firing fifty shells — 2,500 shots in a single day. Over the course of the siege, on average more than 1,000 rounds per day struck the castle's walls. The white plaster was pocked and scarred. The main keep did not fall.

On November 6, 1868 — exactly one month after the encirclement began — Matsudaira Katamori appeared before the imperial commanders and surrendered unconditionally. His life was spared. His domain was dissolved. The Aizu 会津藩 (Aizu-han) ceased to exist. Approximately 2,400 people had died defending it.

The castle itself survived the siege only to be demolished by Meiji government order in 1874. What stands at Aizuwakamatsu today is a concrete reconstruction from 1960. The walls that held through 1,000 shells a day did not survive peace.

Katamori eventually became the head priest of 日光東照宮 (Nikkō Tōshōgū) — the grand shrine of Tokugawa Ieyasu, the first Edo shogun. He spent his remaining years tending the memory of the dynasty he had served. His family's formal reconciliation with the descendants of the Satsuma leaders who had defeated him would not come until the 1990s.