The premise follows Iria, a fearless bounty hunter from another planet, who tracks a ruthless and nearly indestructible alien creature known as Zeiram to Earth. To prevent civilian casualties and contain the threat, she traps the monster within an artificial dimensional construct called the Zone. The plan goes awry when two ordinary Japanese repairmen, Teppei and Kamiya, become accidentally sealed inside the Zone alongside her and the creature, turning a routine capture mission into a desperate fight for survival.

The main protagonist is Iria, a highly skilled and determined interstellar hunter who utilizes advanced weapons, armor, and her trusty computer companion, Bob, to complete her missions. Zeiram is the antagonist, an immortal alien of unknown origin whose physical appearance is that of a large, imposing humanoid wearing a wide, circular hat and a ragged cloak. Its true core is actually a small Noh-like face located on the hat, which is its only weak point. The rest of its body is almost indestructible, capable of rapid regeneration by feeding on organic matter. It extends its core face on a fleshy tentacle to consume victims, absorbing their genetic material to generate smaller, weaker monster clones to do its bidding. Teppei and Kamiya are the two unsuspecting electricians who provide a human perspective, finding themselves caught in a high-tech conflict far beyond their understanding.

The primary setting shifts from a stylized, futuristic version of a Japanese city to the claustrophobic and artificial environment of the Zone. This created dimension serves as the primary battleground, a contained space where Iria and Zeiram are forced into close-quarters combat with the added complication of protecting the two civilians. The narrative arc follows Irias mission as it evolves from a straightforward apprehension into a high-stakes rescue operation. The central conflict is a race against time as Iria must not only find a way to permanently destroy the immortal Zeiram but also protect the two repairmen and find a means of escaping the Zone before they all become permanent casualties of the hunt. The story concludes with a final confrontation where Iria must exploit Zeiram’s single weakness while safeguarding the trapped men.