For many thousand years, Demaon has desired to conquer Earth which is his ideal planet for his demon race. It was widely believed that he was influenced great disaster on Earth such as Cretaceous Paleogene extinction event, the great flood, and the more recently, various natural disaster in modern day. Apparently, Demaon had no interest in recruit any life form on Earth for his cause until met humanity, where he and his kind taught them ancient sorcery which is darker that modern day sorcery.
However, mankind soon learned the darkness within Demaon and banished him and his kind back to his homeworld, but not before Demaon left his dark knowledge in some ancient grimoires that scattered across the world. Nirnaeth was one of the rebelling humans whom documented demons and dark magic's suspectibility with the moonlight, having created a seal on the moon's surface so its power can protect humanity.
Modern Day Invasion
Now Demaon intended to started another invasion again. The time for the invasion finally comes when a desperated woman, Mrs. Mangetsu, contacted him to have her life in exchange for her daughter's recovery. After took her away from Earth and turned her into demon called Medusa, Demaon granted her wish, before making preparations for the invasion for the next few years.
- His name is not appeared in original movie, yet only once in manga.