Anthony is a man with an American father and a deceased Japanese mother living and working in Tokyo. When his son is killed in a car accident, a dark change begins to creep over him, and he starts to transform into metal. He is shot dead by a hitman who is accompanied by a mysterious figure who taunts his dead body. The cryptic man, named Yatsu, then confronts a revived and enraged Anthony, and it’s revealed that the car accident was, in fact, Yatsu’s deliberate act of murder. Anthony tries to turn the tables, firing bullets from his torso in an effort to kill Yatsu, but the villain narrowly escapes.
Yatsu hacks Anthony’s computer to display a cryptic series of scientific documents and instructs him to go to his father’s house, where a secret room is uncovered, filled with files detailing a shadowy Tetsuo Project. Anthony learns that his father met his mother while they were both researching the project. Yuriko arrives, but before she can see her transformed husband, a team of heavily armed mercenaries from a private military company—sent to keep the existence of the Tetsuo Project under wraps—arrives and she is taken hostage. Anthony’s transformation completes its hold and he defeats the PMC team using bullets fired from his body, yet he chooses not to kill them. The severely injured mercenaries are rescued, but are then killed by Yatsu, the film’s own version of the The Metal Fetishist.
Believing he has been possessed by a demon, Anthony attempts suicide with a gun that grows from his hand, but the act fails. He and Yuriko later meet his gravely wounded father, who lays out the truth: Anthony’s mother, disgusted by the militaristic outcome of the Tetsuo Project, joined it to give crippled and sick people new bodies. As cancer claims her, she insists that her husband recreate her as a Tetsuo android so they can still have a child together. That child became Anthony, meaning the living man and his late son were always part of the Tetsuo experiment. The film also reveals that anger is the catalyst for the metal transformation, and that Yatsu murdered Anthony’s son and wounded his father to provoke this change. The elder man bleeds out, and Yatsu kidnaps Yuriko, threatening to detonate a bomb hidden in her necklace if Anthony does not shoot him.
During a chaotic pursuit, Anthony’s rage erupts into a towering metal behemoth with a cannon at its center. Yatsu taunts him to shoot, but a vision of a city in a blazing ball of light if he kills him convinces Anthony to refuse and instead consumes Yatsu whole into his own metal body, then returns to a human form.
Five years pass, and Anthony and Yuriko have a new child and have settled into a calm, contented life. As he stares into a mirror, he recalls Yatsu’s final ominous words: “You don’t want me inside you. You don’t know what I’ll do.” Yet when a group of young thugs tries to intimidate him on the street, he does not surrender to anger; he simply walks past them with quiet confidence, choosing peace over destruction.
