The story follows Kuroi Mato, a young college girl seeking to connect with Yomi Takanashi, one of her classmates who unfortunately seems quite closed to others. One day, the young girl gets the chance to visit her friend and takes the opportunity to share her favorite picture book with her. It is also at Yomi's place that Kuroi meets Kagari Izuriha, a young girl in a wheelchair who is none other than Yomi's best friend. What Kuroi does not know is that there is a world parallel to his, in which the alter ego of every human being lives, and where an incessant war has been going on for a long time. In this world, her own alter ego is called Black Rock Shooter, a young woman with an eye in which burns a mysterious blue flame ... Is there a link between the inhabitants of these two worlds?