C.C. a mystic and beautiful woman or a witch? Its not known what she is, but you can surely say that she isn't human. Or at least it looks quite unlikely. You can rarely meet a green haired cute lady in an anime. She gives the ability Geass to Lelouch and by doing that she not only saves his life, she also changes his destiny. C.C. was a captive of the Holy Empire of Britain. But terrorists kidnap her, and later Suzaku and Lelouch save her. C.C. agrees to help Zero as well as protect him. He owes her for getting the Geass. Its in her interest for him to be alive. That's exactly why C.C. is with Lelouch in some of the tight situations and saves his life a few times. Quite little is known about her past. She is quite the mystic character. Lelouch is not the first to get Geass from C.C. She gave similar abilities to other people as well. One of the things that will make an impression on you is the fact that she loves to eat... pizza.
Translated from bulgarian language by Shakdun (firstname.lastname@example.org)