Kallen Stadtfeld is half Britannian, half Japanese, but believes herself to be a Japanese person at heart and prefers to be known by her mother's maiden name, Kozuki. Her father is Britannian and her mother is an Eleven; her father comes from a prestigious Britannian family, which Kallen benefits from. She attends the Ashford Academy, where she later becomes a member of its student council and is one of its most outstanding students. Her brother, , with whom she had a deep connection, was a former leader of her resistance cell before his death.