"the power of absolute obedience"

- allows him to momentarily control a mind, in a fashion similar to hypnotism, and is situated in his left eye. When activated, a red bird-shaped sigil, similar to the mark on C.C's forehead, lights up in the eye and reaches out to its target(s).
Lelouch's Geass later evolves and becomes permanently activated. Currently, his power evolved over time and became permanently activated, in the second season it is revealed that after Zero and Suzaku's confrontation, Lelouch had his mind wiped by the Emperor and thus does not remember having the Geass, thus the sigil disappears from his eye. When the power of Geass and Lelouch's memories are restored, Lelouch activates and deactivates the Geass by covering his eye with his hand. It's been revealed that his Geass have other psychic powers, including hypnosis.

Lelouch performs some experiments with his power of Geass and discovers the following:

* The user can only use it once on a given individual. Any following attempts will be ineffective.

* The victim is bound by his or her physical and mental capabilities. Asking the victim about or to do something that he or she doesn't know or cannot do will produce no effect.

* Indirect eye contact via a reflective surface, i.e. mirror, will be enough for the power to work.

* The power will work within a 270 meter radius of the user.

* The user may give as many commands as he or she wishes while direct eye contact is maintained.

* The user must give the commands verbally. However, the power of Geass will control the victim for the duration of what the user's command indicates, so the victim may still act under the power's influence even when direct eye contact is broken.

* The user may use the power on as many people as he or she wishes simultaneously, provided that they meet the above rules first.

* The user can also use the power on him or herself, as long as the above limitations and conditions are met.

* The victim will not retain any memories from the time during which he or she is under the influence of the power of Geass due to the rewiring and damage to the brain.

* The power will not work on C.C.

* If the command given is totally repungent to the individual, there will be some initial resistance, even though the command will eventually be carried out. For instance, Princess Euphemia originally resists the carrying out of her command, and seems to be in agony over the thought of it before finally bowing to it's wishes.

Lost Colors incarnation

Rolo possesses a Geass in his right eye, which appears to grant him the ability to temporarily suspend the subjective experience of time for all other individuals within a given sphere of influence -- represented on-screen as a glowing orange bubble that expands from his body. The medium by which the ability affects others is as yet unknown, but consequences of activation are observed in the absence of direct eye contact. The ability's exact limits are similarly unknown, but it seems not to have the single use restriction of Lelouch's Geass. Despite long-term possession of the ability, Rolo appears to remain in full control of its activation.

The Emperor has a Geass marking on both of his eyes. He uses his Geass to erase Lelouch's memories as Zero after Lelouch is captured by Suzaku Kururugi, and to implant false memories of an alternate past. However, C.C. unseals Lelouch's memories after reuniting with him in Babel Tower.

He has the ability to read peoples' minds without direct eye contact. Mao is mentally unstable due to not being able to turn off his power, causing him to hear the thoughts of every person within a radius of 500 meters. He wears headphones repeatedly playing recorded words of encouragement and gratitude from C.C. during his younger days in order to block out the thoughts around him. When Mao finally finds C.C. in Area 11, she tries to get rid of him in an amusement park but fails and Lelouch ends up rescuing her from Mao's chainsaw and using his Geass to make police officers shoot Mao.

Rai's power is the same as that of Lelouch's, "the power of absolute obedience". Like Lelouch, his power is also limited to one use per individual. However, if one individual has already become victim to Lelouch's Geass, he or she is still vulnerable to Rai's Geass, and vice versa. Unlike Lelouch, who requires eye contact for activation, Rai's power uses sound instead of sight, where merely hearing his voiced command is enough for the effect to take place. This allows Rai to more easily use his power on more individuals simultaneously. Yet again, a red, bird-like sigil is seen lighting up when the power is activated, however it does not appear to be from his eye but his mind instead.