essentially, when god was so fed up with humanity, he wanted to create the embodiment of his anger. He first created an empty vessel, known as rai. Rai carried out some missions, but started killing anything and anyone. It turns out that the only pleasure rai gained is from killing people, so god locking it away deep in the aspen forest, one of the most dangerous places in the universe, and placed multiple heavenly guards around it. It eventually escaped however, and eventually ria has to kill it. THIS IS AN ARC IN THE STORYLINE.