Geass is a mysterious ability which certain people can bestow upon others; Zero is the most prominent character who grants the power of Geass. The Geass manifests differently in each individual, possibly related to their inner desires and personality. The power of Geass increases with use, and should the user lack the willpower, they may be consumed by it. Zero calls the Geass the "Power of Kings".
To seek out Zero, One must find the Unknown Kingdom and seek him out. With a test of courage and abilitie, He then will decide wether or not your worthy for The Geass. Geass have endless abilities. Once One obtains Geass, it must get approved by Zero himself under Jutsu List.