There was once a God, Crusader. He was the God of Night, and created the creatures that lurk in the darkness. However, darkness grew inside of Crusader's heart, and he began to create more evil, and twisted dark things. The other Gods began to fear Crusader's power, however, they only watched and waited.
Crusader eventually created a race called Demons. These evil beings began to slaughter and destroy everything in their path, leaving a trail of blood and desruction. The Gods decided to take action, and created a new world, banishing Crusader and the Demons to it. Crusader's powers became severely weakened, no longer being one of the Gods, however, he retained his immortality, and the evil race worshipped him as a God, regardless. He became known as the Demon God.
Crusader eventually escaped his banishment, and brought his demons with him. However, the Gods could do nothing to stop him this time, as Crusader was no longer a God, and they were forbidden to interfere unless another God was the problem. However, the Angels came down to Earth, and there was a great war.
In the end, Crusader went into hiding, as did what remained of his race, and the Angels returned to the sky. Crusader traveled the world, deciding if he was going to enslave the world, and rule as the true God over it, he would need to build and army worthy of such a cause.
Many centuries passed, and the world forgot the great war. By a chance meeting, Crusader met a half Demon named Sara, and soon after, took her as his bride. Crusader bestowed upon her his powers, making her a Demon Goddess. The two had a son years later, named Kuya.
Sara's friend Jem was found raped and murdered when she decided to go visit her old friend, and became filled with rage and hate for mortals. She began a killing spree the likes the world had never seen. Crusader joined in the bloodshed, and together, they brought about the end of the world.
Kuya was left an orphan in a world of ruin, monsters, and humans who would do whatever they could to survive in this new world. The world became a miserable place, but one man took Kuya in, raising him as his own son. Kuya always his the evidence of his heritage, his cat tail and ears.
As time dragged on, Kuya decided that there was only one thing to do to make things right in this world. He would have to find a way to go back in time and stop his parents from bringing about the end of the world.