The Demigod Games: The Daughter of Nemesis

Zeus realize that his own children may overtake him one day. As he and his siblings had done to their own father, Kronus. So he devised a plan to pit the demigods against each other in battles to the death. Of course at first the other gods detested the idea of making their beloved children fight, but when Zeus explained that it would be a fight to determine the best children of the gods, they were all to happy to force their kids to compete.
And so began the demigod games that struck fear into the hearts of half lings around the world.