Introduced as a captive human test subject of the villainous Holy Britannian Empire, C. C. is revealed to be an immortal young woman with special powers called the Geass. Sardonic, stubborn, and mysterious, she can give Geass powers to others, which she does to main protagonist Lelouch Lamperouge. She becomes an ally and protector of Lelouch, at times piloting a mech and leading the paramilitary group the Black Knights to do so. She later assists Lelouch at destroying other Geass users misusing their powers, including her former students, and supports the regime changes that follow.