In the sidestory Nightmare of Nunnally, Mao is the name of a young Chinese girl who deserts the Irregulars. Like them, 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," which allows her to read and manipulate the minds of others through eye contact. In addition to ordinary mind-reading, it allows her to render her victim catatonic by forcing them to relive past experiences, similar to the drug in the anime it is named after. Because C.C.'s cell matter causes cellular breakdown, she seeks to steal Nunnally's bond with Nemo, which she believes to be a possible cure. After Alice breaks Mao's remaining suppressants, Mao lets herself die.