"Old mankind whom Pluto could not defeat, thou art wickedness which violates the dispensation of the universe. The dispensation of the universe is collective. There must exist nothing that standeth in violation. I shall commence purifying the land."
Ancient of Days is a demon in the series.
The Ancient of Days is one of the many names of God, sometimes treated as an avatar of his will. It was first known through the Book of Daniel. It is a name that is meant to represent that God is eternal in Judaism.
The title "Ancient of Days" has been used as a source of inspiration in art and music, denoting the creator's aspects of eternity combined with perfection. In the Zohar, the seminal document of Kabbalah that emerged in 13th Century Spain, there is mention of the Ancient of Ancients, and the Holy Ancient One; Atika Kadisha, variably interpreted as synonymous with the En Sof, the unmanifested godhead.
Shin Megami Tensei IV
In the "Ancient One of the Sun" DLC, following Pluto's defeat at the hands of Flynn and his group, God sends his avatar, the Ancient of Days, to succeed where its predecessor failed. It attacked the remnants of human civilization, destroying what remained of Blasted Tokyo and forcing the survivors to relocate to Pluto Castle.
The White summon Flynn to Blasted Tokyo, intending to show him the despair of the human race. Pluto Castle is attacked by Ancient of Days, prompting Flynn to do battle with it. The Ancient is at first nearly invisible; Burroughs can't even correctly scan him, only getting error messages. She comments it seems as though the Ancient, like Sanat, isn't made of matter native to Blasted Tokyo. It states its mission is "the dispensation of the universe," and insists the old humanity must die to make space for the new one. Halfway through the battle, Kiyoharu runs outside, overjoyed, believing that God's messenger has come to free them from suffering. It makes it clear that it is there to destroy mankind, crushing what little hope he held on to for the last 25 years.
After it is defeated, God speaks to Flynn and Akira, telling them that the former has only defeated one of his forms, and that such trifles will not sway the fate of the world from its course. As multiple cocoons descend from the sky, he tells them that the new humanity will descend upon Blasted Tokyo, and that Genesis has begun. Akira decides that he will negotiate with the new species to seek co-existence and bid Flynn farewell.
The Ancient of Days will only use Diarahan if either of its weaknesses (Electricity or Force) is exploited.