Seven years before the story begins, humanity fought a secret war for its survival against divine beings. To end the conflict, a girl named Waka and her companions were chosen by the gods to become Valkyries, giving their lives to stop the divine threat. Now, Waka’s younger sister Kiko has grown up and is entering high school, trying to live a normal life. However, the divine beings have returned, forcing Kiko to confront the legacy of her sister’s sacrifice and the renewed danger to humanity. The narrative follows Kiko as she navigates high school while becoming entangled in the resurgence of this hidden war, with the Valkyries who once claimed her sister’s life now taking an interest in her. The story is set in a contemporary world where a clandestine battle against supernatural divine entities unfolds beneath the surface of everyday life. Key narrative arcs include the initial revelation of the divine beings’ return, Kiko’s discovery of her connection to the Valkyries, and her struggle to protect the world her sister died for.