Kei Kusanagi's older sister.
In a flashback depicted during a critical 'standstill,' it is revealed that Kozue was an exceptionally intelligent, yet potentially mentally unstable girl. She believed that human emotions were the root cause of much suffering in the world and sought to escape them by taking her own life, an event which Kei tragically witnessed. The trauma from this experience, coupled with the guilt he felt for being unable to prevent her suicide, triggered his first 'standstill.'









