Kyoko Akizuki is Nobuhiko's younger sister, targeted a number of times by the High Priests as her life-force could awaken Shadow Moon. At first she was not aware of Kohtaro being Black until she was abducted by the Birugenia and saved by him. Once Nobuhiko emerges as Shadow Moon, she and Katsumi are terrified of his new appearance as she eagerly refuses his offer to join him in making a new world without violence. After the defeat of Shadow Moon at the hands of Black, she and Katsumi left Japan to start a new life abroad.