In most of Japan, a 薙刀 (naginata) — the curved-bladed pole weapon, longer than a sword, heavier than a spear — was kept in the household for ceremony or as a decorative symbol of a samurai family's status. In Aizu domain, it was a training weapon. Girls in samurai families picked it up young and drilled with it throughout their lives. The domain's founding code, the 什の掟 (Jū no Okite), demanded discipline and readiness from every member of the warrior class, regardless of gender. When the crisis came, this was not abstract philosophy.

The crisis came in October 1868. The imperial army — the Satchō Alliance that had overthrown the Tokugawa shogunate and launched the 戊辰戦争 (Boshin Sensō) — surrounded 鶴ヶ城 (Tsurugajō, Tsuruga Castle) in Aizuwakamatsu on October 6. Inside the walls: approximately 5,000 people. Samurai, women, children, elderly, servants. No possibility of outside relief. And the bombardment began — averaging over a thousand cannon shots per day, every day, for a month.

The women inside the castle did not shelter and wait. They kept the garrison functioning. They hauled water through artillery fire. They melted the lead and tile from the roofs over their own heads to cast into buckshot for the defenders. They treated the wounded in rooms so crowded with the injured that there was nowhere left to lay a man down. Some women killed their own mothers-in-law and young children to spare them the prospect of capture, then walked to the front lines.

Outside the castle, a group of women formed their own fighting unit without the domain's authorization. The 娘子隊 (Jōshitai, Women's Corps) assembled under a 21-year-old martial arts instructor who had trained for combat her entire life and saw no reason to stand aside now. Aizu's male commanders denied them official status — women were not to be enlisted as soldiers. The women went to the front line anyway. On October 16, 1868, their leader charged imperial troops near Yanagi Bridge in the Nishibata area. She was shot through the chest. Her dying instruction to her sister, Yūko: cut off my head. Do not let them take it as a trophy. Her head was carried to 法界寺 (Hōkaji Temple) and buried under a pine tree, where a memorial stands today.

Meanwhile, inside the castle, Yamamoto Yaeko (山本八重) — 22 years old, trained in gunnery by her brother before he was killed — had abandoned naginata for firepower. She commanded artillery units. She taught boys marksmanship. At night, she dressed in her dead brother Saburō's uniform and crept outside the walls, Spencer repeating carbine in hand, to snipe at imperial positions in the dark. She was not asked to do any of this. It was simply what the moment required, and she had been prepared.

The castle held until November 6, 1868. When it finally surrendered, the 娘子隊 (Jōshitai) was never officially listed among Aizu's military forces. The women who fought had no rank, no record, no formal acknowledgment from the domain they bled for. History gave them one anyway.