Observer

An Observer (観測者 Kansokusha) is a person who is able to create Phenomenon Interventions by acknowledging a reality and using their will to enforce it; this ability is succinctly called Observing. There are several Observers, and although they have great power, to wield it is also risky.

Information
Observers have the unique ability to use Phenomenon Intervention, a technique that can allow them to freeze time and even manipulate reality around them as they perceive it. When one is Observed, they are fixed into reality, becoming what they are Observed to be; Arakune, a being of pure seithr, was Observed to be in his liquid state by Kokonoe - seithr usually evaporates after a set time, but Kokonoe's Observation prevented his death. Subjects can have multiple Observers, and combat is one of the best ways for an Observer to strengthen their recognition of a target. All known Onlookers are Observers.

Observing is dangerous, however, as the Observer needs to constantly Observe themselves and their target to maintain their existences. Without doing so, they will vanish. Machinery and Ars Magus can be used to amplify one's Observation, but it is not a reliable method; furthermore, an Overdrive can be used to alleviate the burden of Observing, but it is dangerous.

Observers

 * The Origin - the wielder of the Amaterasu Unit; the most powerful of all Observers
 * Takamagahara - Observed Terumi
 * Noel Vermillion/Mu-12 - the Successor of the Azure; Observed Terumi, Tsubaki Yayoi, and Nu-13
 * Rachel Alucard - also an Onlooker; Observed Hakumen
 * Amane Nishiki - also an Onlooker; offered to observe Ragna the Bloodedge
 * Clavis Alucard - also an Onlooker; has not Observed a target but uses Phenomenon Intervention
 * Kokonoe - Observed Arakune, and Hakumen
 * Relius Clover - Observed Arakune
 * Izanami - Observed Terumi
 * Yuuki Terumi - often Observes himself to maintain his existence
 * Litchi Faye-Ling - a weak Observer who amplifies it with technology; Observed Arakune

Observer
''Those who Observe a subject. 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.''

Currently known Observers include Rachel and Kokonoe.

Trivia

 * In the English localization, Onlooker was merged with Observer, taking on the latter's name.