The story follows young Mato Kuroi, who just entered junior high school. On her first day, she notices a classmate named Yomi Takanashi, and the two quickly become friends. Mato is innocent and naive, while Yomi is mature and level-headed; together they form a strong bond. As they advance to their second year, they are placed in separate classes and begin to drift apart, yet a deep friendship lingers. In another world, the same girl appears as Black Rock Shooter, a blue‑eyed warrior wielding a blazing sword. She faces off against Dead Master, a mysterious girl who wields a jet‑black scythe. Their battle is fierce and deadly, mirroring the complex emotions and connections from Mato and Yomi's story.