Kallen Stadtfeld is a Britannian-Eleven girl who goes by her Britannian name when attending Ashford Academy, where she pretends to be ill to explain her prolonged absences. She believes herself to be Japanese at heart and prefers to be known by her birth name, Kallen Kouzuki. Kallen is a member of a Japanese resistance cell led by her brother, who died prior to the first episode, and later joins Zero's Black Knights. She is the group's most talented pilot and on par with the Knights of the Round. She pilots the unique Guren Mk-II. Her devotion to Zero is unmatched among the rest of the Black Knights.