Calamity Trigger

The Calamity Trigger, also known as the Successor of the Blue (蒼の継承者), is the title of the one who inherited the true Blue. The Successor is a perfected Dimensional Boundary Contact Prime Field.

The Successor of the Blue can watch the world with the Power of the Eye and is the only being capable of locating the Amaterasu Unit within the infinite reaches of the Boundary.

The Successor in the original world was the Origin, which is the wielder of the Master Unit, Amaterasu.

Mu-12, more commonly known as Noel Vermillion, became the Calamity Trigger when she broke the timeloops by saving Ragna the Bloodedge from falling into the Kiln.

Nu-13, after the process of assimilation between her and Noel, gained all her memories, became a false Successor, and was able to open the Nemesis Horizon and summon the Master Unit.

Judging by the name of a save file, Es became a Successor after Hinata Himezuru transferred the Embryo to her.