Abe no Seimei is based on the historic figure of the same name. He is the son of Hagoromo-Gitsune, and is considered to have been a legendary onmyouji of the Heian Era. Said to preside over the systems of divination, the calendar, astronomy and time-keeping in his position as the chief court astronomer, he was fiercely trusted by nobles of the time and considered a genius for his magical ability. At the same time, he was considered to be a sorceror of black magic, said to be extremely knowledgable about forbidden arts, using hexes to kill people and manipulation techniques that could control ayakashi and other demons.
A thousand years ago, he sought a way to perfect a resurrection technique which would allow him to live forever through reincarnation. He realized that the only way it could be done would be through his mother repeatedly giving birth to him (thanks to her own ability to reincarnate). His original reason for wanting eternal life stemmed from his desire to create a perfect world for both humans and ayakashi. However, his goal changed after court noble Chief Advisor Yorimichi murdered the "Shinoda Fox," having heard that one could achieve eternal youth by eating its liver. Not knowing that the fox was in fact Seimei's mother, Yorimichi entrusted Seimei with the task of creating an elixir of life from the fox's arrow-riddled body. Enraged, Seimei slaughtered all the court members present and left, carrying his mother's dead body. Some time after that, he became known as the Nue.