a long time ago humans and demons live in the same dimension, demons have overpowered the humans and that's caused the human almost extinct before a man that has a book of power and wisdom make him became immortal and capable to send them to the other dimension after that he becomes the hero and teaches mankind to protect themself from the demons and he protects the book because the demon can intervene in a human world by possessed human and using the book to travel them into the human world but they cannot directly harm human until a group of people who deceived by the demon that disguise as a hero found the hero and killed him(but the hero cannot die) and he used the book of power and wisdom to release the demons to the human space and time, humans cannot defeat the demon because they abandoning the way of life of the hero cause them to become weaker mentally and physically and they have to survive until the hero resurrected or becoming demons slave