In a world veiled in mystery, Black★Rock Shooter, a girl with jet-black hair and a glowing blue eye, wields a massive cannon in intense battles. Meanwhile, in a different realm, middle-schooler Mato Kuroi befriends Yomi Takanashi, a classmate with a unique name. Despite Yomi's initial reluctance, Mato persists with the help of her supportive friend Yū Kōtari. Alongside quirky individuals like counselor Saya Irino and spirited club captain Arata Kohata, Mato's world expands. When a chance encounter over a beloved picture book, 'Li'l Birds At Play,' leads to a visit to Yomi's home, their friendship blossoms. However, a new presence, Kagari Izuriha, Yomi's wheelchair-bound best friend, adds complexity to their bond. Amidst these interconnected worlds, the tale of Mato and Black★Rock Shooter unravels, delving deep into their shared 'pain'.