Doomsday (滅日 Horobi, Day of Destruction) is a phenomena event that was brought about by Yūki Terumi and Hades: Izanami. Originally, Takamagahara wished to bring about the event, however, their chance was stolen by the aforementioned duo following Takamagahara's demise.
The Doomsday is a ceremony which effectively heralds the end of the world, and begins the construction of a new one. The ceremony begins with the souls of the living being returned to the Azure; following this, the world is reset (初期化), and, finally, the Successor of the Azure begins to reconstruct the world. The Entitled, however, still remain in the world as they have been chosen by the Azure.