Mao (マオ) is a character that only appears in Nightmare of Nunnally. She has a Geass ability granted by an infusion of cell matter from C.C. A Geass sigil lights up in her left eye when she uses it. Her Geass ability is known as "The Refrain," (マオリフレイン, Maorifurein) which allows her to read and manipulate the minds of others through eye contact.