The Revelation of Saint Ioánnis is an ancient document described by Seshat and Toujirou as a prophecy for how the world ends.
The Revelation was the 27th book in a series of canonical scriptures as described by the Muratorian Canon, and by the time the Council of Carthage met, the Revelation had been deemed non-canon and thus removed. However, the Revelation had also been "deleted" from history, with an unknown person or organization trying to bring about the prophecy described within. The Order of Prometheus is attempting to stop them.
It is implied that the Revelation may be the Book of Revelations, the 27th book in the New Testament of the Bible. "Ioánnis" can be written as John, who is the supposed author of the original Book of Revelations.