In 2005, a group of Japanese archaeologists are on a quest, delving into the tunnels of Iwo Jima, where they unearth letters long buried beneath the soil. The narrative then shifts back to 1944, amidst the harrowing backdrop of war. Here we meet Private Saigo, a conscripted baker who finds himself at the mercy of his commanding officer Captain Tanida. After voicing a rather pragmatic opinion that perhaps it would be better to hand the island over to the Americans, Saigo is met with severe reprimand. Fortunately, the arrival of General Tadamichi Kuribayashi, portrayed by Ken Watanabe, interferes, as he takes command of the beleaguered garrison.
Kuribayashi learns shockingly from Colonel Baron Takeichi Nishi that the Japanese Combined Fleet, a critical source of support for the island, has been decimated. Faced with this grim reality, he immediately orders the garrison to begin constructing a series of tunnels for defense, despite protests from his subordinate officers regarding the absence of beach fortifications. In February 1945, the first wave of American air assaults begins, leading to a full-scale invasion where U.S. Marines land on the island.
In a moment of tactical ingenuity, Kuribayashi waits for the beach to be swarming with Marines before unleashing his men to open fire. Although the Marines suffer severe casualties, they quickly overcome the beach defenses, prompting the battle to shift to the labyrinthine tunnels beneath Mount Suribachi. A significant moment occurs when Saigo inadvertently overhears Colonel Adachi fervently pleading with Kuribayashi for permission to end his life, a request that Kuribayashi steadfastly denies.
Amidst the chaos, Adachi ultimately disregards the General’s orders, influencing his men to commit suicide. Under Tanida's command, soldiers resort to desperate measures, using hand grenades against their own bodies while Tanida himself chooses a tragic end. Meanwhile, Saigo persuades Shimizu, another soldier, that serving the Emperor requires them to continue fighting rather than surrender. They join a dwindling group of survivors, one of whom meets a horrific fate at the hands of a U.S. Marine wielding a flamethrower.
Their situation becomes increasingly dire when Lieutenant Ito, a fanatical Navy officer, threatens to execute them for their perceived cowardice. However, Kuribayashi intervenes, reproving Ito for such rashness and reiterating his orders to evacuate Mount Suribachi. In a moment of despair, Ito straps explosives to himself, intent on sacrificing himself amidst the battle.
As the scenario unfolds, Saigo boldly declares his intention to surrender, challenging Shimizu to arrest him for his actions. To his surprise, Shimizu reveals that he has been dishonorably discharged from the Kempeitai for not following a cruel command, which creates a bond of friendship between the two.
As the conflict escalates, Nishi suffers grave injuries and ultimately takes his own life when he finds himself isolated. In a desperate bid for survival, Shimizu and Saigo endeavor to surrender together, but their plans are thwarted when they are discovered. Shimizu is forced to surrender to an American patrol, which tragically results in his death as the guards, fearing escape, take fatal action against him and another Japanese prisoner.
Meanwhile, a desperate Lieutenant Ito surrenders, leaving Kuribayashi and his dwindling forces to face the overwhelming might of the Americans. After a final charge, Kuribayashi is critically wounded, and in a poignant moment, he orders his loyal aide, Fujita, to behead him to avoid capture. As Fujita is shot by a Marine sniper, Kuribayashi calls upon Saigo to bury him, ensuring that his body will not be recovered by the enemy.
In the film's heart-wrenching climax, Kuribayashi, finding an M1911 pistol given to him by a friend, questions, “Is this still Japanese soil?” to which Saigo affirms, “Yes, this is still Japan.” With sorrowful resolve, Kuribayashi takes his own life, leaving Saigo to drag him away for a respectful burial.
As the dust of battle settles, a Marine patrol stumbles upon the bodies of the fallen soldiers. In a moment of compassion, they choose not to kill Saigo, who is weak and despondent; instead, they carry him off to a POW camp. As he regains consciousness, Saigo reflects upon the setting sun over the island’s black sands, revealing a grim smile.
The narrative concludes with the archaeologists uncovering the letters that Saigo had so thoughtfully buried, encapsulating the lingering echoes of sacrifice and honor amid the ravages of war.
