Observer

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

It is unknown how one actually becomes an Observer, but someone can actually agree to be Observed by another individual. They must always perceive themselves, and must constantly perceive the "existence" of their target subject. If not, they would instantly vanish, along with the "existence" they are Observing. 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.

Known Observers

 * The Origin — wielder of the Amaterasu Unit, the most powerful Observer who can rewrite events,
 * Takamagahara System — Observed Yūki Terumi who was released by them,
 * Kokonoe Mercury — Observed Arakune, temporarily Hakumen, as she could not revive him in full out of the Boundary, then TR-0009 Tager, Lambda -No. 11-, and Celica A. Mercury,
 * Rachel Alucard — former Amatsumugi, formerly Observed Hakumen,
 * Litchi Faye Ling — Observed Arakune, however her Observation force was weak and was strengthened by machinery,
 * Relius Clover — temporarily Observed Arakune,
 * Noel Vermillion — unknowingly Observed Terumi, and temporarily Observed Tsubaki to save her from Mind Eater, unwarily Observed Nu -No. 13- as herself,
 * Hades: Izanami — temporarily Observed Terumi, triggered massive-scale Event Interference with the usage of Takamagahara System's power during BlazBlue: Chronophantasma events,
 * Yūki Terumi — it's unknown if he had any Observation targets; people's hatred for him works like Observation,
 * Amane Nishiki — wanted to Observe Ragna to slow down the process of him becoming the Black Beast.

Trivia

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