When Zero is planning to attack the Britannian Art Gallery with the goal of assassinating the Emperor who has arrived there, Kallen confronted him about whether it would be a trap and also commented that she would still follow him. Admiring her answer and loyalty, Lelouch placed a geass command on her that if anything would happen to him then she would lead the Black Knights. When the Black Knights took the Art Gallery hostage, she is confronted by Suzaku and was surprised that she's not only a member but a half Britannian-Japanese right after he left to stop Zero from killing the Emperor. After Lelouch was captured and accused for killing the Emperor, Kallen assume leadership of the Black Knights as the new Zero and later led the remaining Black Knight members to begin an assault on the Governor Building of Area 11, unaware that Lelouch is freed by Suzaku and are both planning to stop Schneizel.