Saigō Takamori (西郷 隆盛, Saigō Takamori) did not believe he was fighting the Emperor. He believed he was rescuing him.

The Meiji government had, in Saigō's view, been captured by corrupt ministers and foreign-influenced bureaucrats who had betrayed the principles of the Restoration they had all fought to achieve. The former samurai class — the 士族 (shizoku) — had been stripped of their stipends, forbidden to wear swords by the Haitorei (廃刀令, Haitorei) edict of 1876, and replaced in Japan's military by conscript peasants with rifles. Everything that had defined the warrior class for seven centuries had been legislated out of existence. The men who had sacrificed most to bring the Meiji era into being had received, as their reward, their own erasure.

Saigō had returned to Kagoshima in 1873 after resigning from the government over the cancellation of a planned Korean expedition. He established private military academies — the Shigakkō (私学校, Shigakkō) — where former samurai trained, drilled, and simmered. The government in Tōkyō watched with growing alarm. In January 1877, Imperial agents were caught attempting to remove weapons stockpiles from Kagoshima arsenals. Saigō's students seized the arsenals first. The rebellion had a trigger.

On February 15, 1877, Saigō marched north from Kagoshima with roughly 12,000 to 15,000 men — the size varying by the point in the march — through a snowstorm that contemporaries called the worst in fifty years. The column moved along frozen roads, breath clouding in the cold air, armed with a mix of modern rifles and the curved swords their grandfathers had carried. The plan was to reach Tōkyō and present the Emperor directly with their grievances. Between them and Tōkyō stood Kumamoto Castle.

Kumamoto Castle (熊本城, Kumamoto-jō) had been built by the daimyo (大名, daimyō) Katō Kiyomasa (加藤 清正, Katō Kiyomasa) in 1607, during the years when castle architecture in Japan reached its pinnacle. Its walls curved inward at the base — the characteristic mushagaeshi (武者返し, mushagaeshi) slope that made scaling impossible. Kiyomasa had reportedly designed it to withstand a three-year siege. In 1877, it was the Imperial Army's primary garrison fortress in Kyushu, and it sat directly astride the road north.

The rebels had to take it or leave a fortified enemy army in their rear. They chose to take it.

On February 19, 1877, the first shots of the Satsuma Rebellion were fired when castle sentries opened fire on Satsuma advance units probing the outer defenses. Major General Tani Tateki (谷 干城, Tani Tateki), commanding 3,800 regular soldiers and 600 police inside, had one significant advantage he kept carefully concealed: the loyalty of his officers was not certain. Many of his garrison men were Kyushu natives — Kagoshima-born officers who knew Saigō, had trained under him, revered him. Tani concluded that his men would hold defensive positions but might fracture if ordered to advance and fight their former teachers hand-to-hand. He chose strict defense.

The castle's keep (天守閣, tenshukaku) burned in the opening fighting — the cause never determined, possibly arson, possibly accident. The main palace followed. When the smoke cleared, Tani's garrison held the stone walls and foundations of a gutted fortress. They would defend those ruins for 54 days.

On February 22, the main Satsuma army arrived and attacked in a coordinated pincer movement from multiple directions. The walls absorbed the assault. By approximately February 25, after two days of direct attacks that produced casualties but no breach, the Satsuma commanders shifted strategy: encircle the castle completely, cut off supply lines, and wait for starvation to do what assault could not.

The defenders were already hungry. A warehouse fire — cause uncertain — had depleted the garrison's food stores just before the rebellion began. The besieged men were eating through diminishing reserves from the first week.

Among the officers inside those walls: Nogi Maresuke (乃木 希典, Nogi Maresuke), future general and national hero of the Russo-Japanese War. Kodama Gentarō (児玉 源太郎, Kodama Gentarō), who would serve as chief of staff in the same war. Kawakami Sōroku (川上 操六, Kawakami Sōroku) and Kabayama Sukenori (樺山 資紀, Kabayama Sukenori). A remarkable concentration of future military talent, all forged in the same fifty-four days of cold and hunger and daily skirmishing — all of them tested by the last great samurai army Japan would ever field.

Nogi, notably, lost his regiment's battle standard during the fighting — the Emperor's banner, an almost unthinkable disgrace for an Imperial officer. He carried that loss for the rest of his life, listing it among the reasons for his eventual ritual suicide on the day of Emperor Meiji's funeral in 1912.

The siege of Kumamoto Castle ended on April 12, 1877, when Imperial relief forces broke through at the Battle of Tabaruzaka (田原坂の戦い, Tabaruzaka no Tatakai). The Satsuma army, denied the castle's supplies and now cut off from reinforcement, began its retreat south. The rebellion dragged on through summer — skirmish by skirmish, position by position, the samurai army shrinking, its ammunition depleted, its men increasingly fighting with swords against soldiers with rifles and artillery.

Saigō Takamori died on September 24, 1877, at Shiroyama (城山, Shiroyama) near Kagoshima, surrounded by 30,000 Imperial troops. Wounded in the thigh and abdomen in the final charge, he asked a companion to help him perform 介錯 (kaishaku) — the beheading that completed a seppuku (切腹, seppuku) death. He was 49 years old.

The Satsuma Rebellion was the last major armed resistance by the samurai class. The 士族 (shizoku) had fought, and lost, and the question was answered permanently: peasant conscripts with modern rifles would defeat samurai with swords and spirit, every time. The class that had governed Japan for seven centuries as its warrior elite was finished.

Kumamoto Castle was rebuilt in the 1960s in concrete and badly damaged in the 2016 Kumamoto earthquakes. Restoration work continues. The curved stone walls — Kiyomasa's original mushagaeshi — still stand.