Legend of DUO

In 2000s, human beings have lost their purana, which are essential for living thing. It means that the human species is goinig to die. However, there is a vampire who saves human beings from extinction by revealing the secret of purana. In a mythical era, there was a god who was punished eternally because he had brought the fire to the human beings. Like him, the vampire will be punished because he breaks the taboo to tell the secret of purana to human beings. That vampire is named Duo, and the vampire who punish him is Zieg. They used to be good friends...