The world is beset by the appearance of monstrous creatures, but one of them may be the only one who can save humanity.

The island of Iwo Jima stands between the American military force and the home islands of Japan. Therefore the Imperial Japanese Army is desperate to prevent it from falling into American hands and providing a launching point for an invasion of Japan. General Tadamichi Kuribayashi is given command of the forces on the island and sets out to prepare for the imminent attack. General Kuribayashi, however, does not favor the rigid traditional approach recommended by his subordinates, and resentment and resistance fester among his staff. In the lower echelons, a young soldier, Saigo, a poor baker in civilian life, strives with his friends to survive the harsh regime of the Japanese army itself, all the while knowing that a fierce battle looms. When the American invasion begins, both Kuribayashi and Saigo find strength, honor, courage, and horrors beyond imagination.

In the 1870s, Captain Nathan Algren, a cynical veteran of the American Civil war who will work for anyone, is hired by Americans who want lucrative contracts with the Emperor of Japan to train the peasant conscripts for the first standing imperial army in modern warfare using firearms. The imperial Omura cabinet's first priority is to repress a rebellion of traditionalist Samurai -hereditary warriors- who remain devoted to the sacred dynasty but reject the Westernizing policy and even refuse firearms. Yet when his ill-prepared superior force sets out too soon, their panic allows the sword-wielding samurai to crush them. Badly wounded Algren's courageous stand makes the samurai leader Katsumoto spare his life; once nursed to health he learns to know and respect the old Japanese way, and participates as advisor in Katsumoto's failed attempt to save the Bushido tradition, but Omura gets repressive laws enacted- he must now choose to honor his loyalty to one of the embittered sides when the conflict returns to the battlefield...