Thor and Rai Klein, 11-year-old twin boys, are forced away from their home planet when their parents are murdered. They awaken on the terraformed planet of Chimaera, where carnivorous plants predominate and the few humans who live there are divided into four groups known as "Rings." They soon meet a young man named Zagi, and the twins learn that only the "Jyu Oh Sei"—the one who conquers these four Rings—is allowed to leave the planet. Thor vows to live in Chimaera's harsh, brutal environment in order to return home and find the truth behind his parents' deaths. However, he rapidly discovers that there is more to this odd environment than meets the eye.