Mato Kuroi discovers Yomi Takanashi on her first day of junior high and is immediately drawn to the timid and introverted girl. Despite some initial reluctance, Mato persists in her efforts to befriend Yomi and forge a strong bond with her. A significant moment in their relationship occurs when Yomi expresses an interest in Mato's phone, which is adorned with a cute blue bird, leading to a shared love of the "Li'l Birds At Play" book and strengthening their connection. Meanwhile, in a parallel dimension, Mato and Yomi take on different identities as Black★Rock Shooter and Dead Master, respectively. The unforeseeable actions of the girls in this alternate universe have a significant impact on their real-life counterparts' world, without their knowledge. Mato and Yomi's paths become intertwined as they become entangled in a complicated, unknown web of events, guided by destiny's threads.