Geass, also referred to as the Power of King , is a mysterious ability which certain people can bestow upon others (the word itself potentially being an intentional corruption of geas or geis, a type of magical contract in Irish mythology). According to an English edition of Newtype, the power of Geass has something to do with the very existence of humankind and it may be used to destroy or transform just about Cosplay Costumes. It is represented by a bird-shaped symbol which glows red when active.

Every Geass power has its own unique set of both abilities and limitations (for example, Lelouch’s power, the ability to make anyone obey him, can only be used once on a given person), allowing for their defeat or victory by someone who is aware of its characteristics. According to C.C. in the anime series, the way geass manifests itself in a person is determined by the person’s deepest/truest desire (e.g. C.C.’s Code Geass Cosplay  made everyone love her in response to her desire to be accepted and loved). Further understanding of the power of Geass even leads to the development of a device that can undo its effects. All Geass abilities that have thus far appeared within canon of the anime series have been related to the mind, influencing things such as emotion, perception, and memory.

Immortals have their own set of powers aside from those related to Geass. They are able to project images into the minds of others, causing them to hallucinate. Immortals seem to be able to tell whether a person has received Geass from another or not, and to open a telepathic communication channel among themselves (but this is consensual; even though C.C. is able to converse with V.V. in the first season, she is unable to track him down). Their origin and relationship to the world of C, the latter being a main concept of the series related to the collective unconscious of the mankind, is unexplained, as are their intentions. Events inside the world of C suggest the possibility of communicating with the departed Cosplay Long Wigs(as the Emperor claims to be able to talk to his deceased son while inside it). This and Suzaku Kururugi’s peculiar reactions to and ability to detect the presence of Immortals indicate that there is more to Immortals and Geass than has been revealed so far.