Title: Juu Ou Sei
English title: Jyu-Oh-Sei: Planet of the Beast King

After the murder of their parents, 11-year-old twin brothers Thor and Rai Klein are sent away from their home planet. They find themselves awakening on the terraformed planet of Chimaera, where carnivorous plants dominate and the few humans who live there are divided into four groups known as "Rings." Soon after, they meet a young man by the name of Zagi, and the twins learn that only the "Jyu Oh Sei"—the one who conquers these four Rings—is allowed to leave the planet. 

Driven by the desire to return home and discover the truth behind the death of his parents, Thor resolves to survive in the harsh, merciless environment of Chimaera. However, he quickly learns there is more than meets the eye in this strange ecosystem. As Thor is swept up in the politics that entangle the Rings, he uncovers more about his parents' murder, and ultimately, humanity's fate as a whole.