AD 2436. Thor and Rai are twins who've been raised in the space colony Yuno, of the Vulcan Federation Government, 150 light-years away from Earth. Their parents are killed in a horrific manner, and they are sent to the "Jyu Oh Sei", or the Planet of Beasts, by the Federation Army. Jyu Oh Sei, whose actual name is Chimera, is a prison planet for ferocious criminals where only the most ferocious 'beasts' can survive.

There are 4 communities on the planet, Blanc Ring, Sun Ring, Nights Ring, and Ocle Ring. They are divided by their skin colours.

Jyu Oh, the King of Beasts, is the top dog chosen from each community, and they rule Chimera as kings. In order to avenge the murder of their parents, and to discover the truth behind that event, Thor aims for the position of Jyu Oh.