The demonic world feeds off of negative energy, such as hate, anger, fear, from the human world. All the negative energy builds a black sun, which nourishes all the demons who live there. When the sun killed the Demon King and many of the demon lords because of too much energy, the top commander of the demonic world, Julia, decided to venture to the human world and purify it. So she took on human form and met a wimpy college student, and made a contract with him to rid the world of negative energy. Positive Energy, starting with me!