Okay, first of all, I want to rank this anime 8/10. Why? Well, the animation was good, the plot were good but the pairings/couple were pretty bad (in my opinion).
Here goes the story, Thor, the protagonist lived in space with his parents and his twin brother Rai. But for some reason, his father were against the man who runs their planet and they were murdered (which I thought at first). As a result, the twins weren't murdered but instead they were thrown out to Prison Planet~ Chimera (as planned, you must watch the anime or read the manga...to prevent the series to be spoiled.. lol).
Chimera, full of murderous people, who have laws on their own, and seek for ultimate survivors, some are cannibals and just plain bloodthirsty murderers, not just that, the place are filled will man-eating plants.
At first, Thor was optimistic that they can go back and avenge their parents deaths but somehow, a man who just saved them told him that if Thor hangs around with his twin, he might be a burden and can cause his own death.
Thor, thinking too much about what the man had said, came to him the intent to kill his brother, Rai being pessimistic about everything and as if he's world revolves around only with Thor, drives Thor "crazy". Thor attempted to kill Rai, but, because of Rai's plead, his senses came back but it was too late, they were surrounded with man-eating plants, the land crumbles and it started to eat them, somehow few people arrived and came to the rescue... but Rai couldn't make it, he was strangled with the veins and unfortunately buried him to death (or he could be eaten afterwards... who knows).
Thor was shocked and felt guilty of actually trying to kill his brother. Thor, faced the truth and focused on one goal, to leave and go back to his planet. But its not that simply, you must have the rank of Jyu Oh, meaning, (as I can remember, watch the series 4-5 years ago..) 1st he must acquire the top of which he conquered RING, since there are 5 rings in Chimera. He must defeat all tops of the 5 rings, so that, he can be the "Jyu Oh" who can only go in/out of Chimera.
But before Thor can be the top and further become the Jyu oh, he had to face many obstacles and challenges, along with those people who helped him, which somehow one of them cannot be trusted on, which eventually helped him made to the top.