|Aliases||紅月 カレン, Kouzuki Karen|
|Hair||Curtained, No Bangs, Parted in Middle, Red, Shoulder-length, Spiky, Straight|
|Body||Pale, Slim, Teen|
|Clothes||Belt, Crop Top, Detached Sleeves, Headband, Leg Warmers, Miniskirt, Peaked Cap, School Uniform, Shorts, Thigh-high Stockings, Trench Coat, Turtleneck Tank Top|
|Role||Comrade, Half-Japanese, Honor Student, Mecha Pilot, Revolutionary, Secret Identity, Student Council Member|
|Visual novels||Main character - Code Geass ~Hangyaku no Lelouch~ Lost Colors|
|Voiced by||Koshimizu Ami|
Kallen Stadtfeld is a half-Britannian, half-Japanese teenage girl. Her father is Britannian and her mother is an Eleven; her father comes from a prestigious Britannian family, known as the Stadtfeld family, which Kallen benefits from. She attends the Ashford Academy, where she pretends to be a sickly, milquetoast student to explain her prolonged absences and changes her appearance. She later becomes a member of its student council and one of the school's most outstanding students. In school, she is known by her legal name but she prefers her mother's maiden name, and goes by the alias Kallen Kouzuki during her revolutionary activities. Kallen is initially a member of a Japanese resistance cell led by Ohgi, using her brother's death as motivation, and later joins Zero's Black Knights. She is the group's most talented pilot and on par with the Knights of the Round. Throughout the series, her devotion to Zero is unmatched among any of the other members of the Black Knights, almost being Lelouch's female counterpart. Conversely, she dislikes Lelouch, despite constant remarks from others about intimacy in their relationship, and is dismayed when her Knightmare rival, Suzaku, reveals that Lelouch and Zero are the same person. However, when she learns more about Lelouch's noble desires via C.C. and Nunnally, she helps protect his identity and ultimately develops feelings for him.