Zoids: Chaotic Century is set in the far reaches of the Milky Way, on the planet Zi. On Zi, there are metallic life-forms known as Zoids, which possess powerful fighting capabilities. Throughout the recent history of the series, Zoids have been used as weapons in an ongoing war between the Helic Republic and Guylos Empire. The setting of Chaotic Century is a few years after the most recent war between the Helic Republic and the Guylos Empire. The two nations are currently observing a ceasefire, although ambushes and minor assaults are initiated by both sides, and tensions are high after it is revealed that one or both sides may have access to the ancient technology of the Ancient Zoidians. The series follows the story of Van Flyheight, a teenage boy who discovers a mysterious girl named Fiona (Fine in the Japanese version), and an Organoid named Zeke (Sieg). Van discovers that Zeke has the ability to merge with a Zoid, increasing its fighting power, and with that skill, Van and Fiona set off to discover the secrets of Fiona's past. During their travel, they meet up with a transporter named Moonbay, and a mercenary named Irvine, who initially thwarts their progress, but eventually begins traveling with them. As they travel across the Helic Republic, a new war breaks out, with the group of travelers being caught in the middle of it.