Observer

An Observer (観測者), by simple terms, is someone who creates Phenomenon Interventions by acknowledging what they see.

It is unknown how one actually becomes an Observer. Someone can actually agree to be Observed by another individual.

An Observer must observe themselves at anytime or they would disappear. Special beings like Yūki Terumi or Hakumen will disappear without an Observer. Inexperienced Observers (such as Kokonoe) have no choice but to continue Observing themselves and others in order maintain their own existence. Those with very little experience, such as Litchi, may be forced to have their abilities as an Observer strengthened by machinery.

The idea of an Observer is based on quantum physics, the Schrödinger's cat experiment and Many-worlds interpretation.

List of known Observers

 * Amaterasu - observes the whole world; she can interfere and rewrite events.
 * Takamagahara - the system observed the Boundary, where Amaterasu was placed, and Yūki Terumi; they were responsible for rewinding the time from 2200 AD back to 2100 AD.
 * Kokonoe Mercury - observes Tager and Arakune, and formerly Lambda.
 * Litchi Faye-Ling - observes Arakune, however her observation force is weak.
 * Relius Clover - observes Arakune.
 * Rachel Alucard - the former Observer of the Boundary (境界の観測者), entitled as Amatsumugi (アマツムギ); formerly observed Hakumen.
 * Noel Vermillion/Mu -No.12- - temporarily observed Terumi and Tsubaki.
 * Hades Izanami - temporarily observed Terumi.
 * Yūki Terumi - does not observe anyone, but has ability of doing it; people's hatred for him works like observation.