During her first day at junior high, Mato Kuroi befriends Yomi Takanashi despite their initial differences. The two grow inseparable, exchanging matching blue star charms to symbolize their bond. However, as they enter their second year, Mato's newfound friendship with Yuu Koutari causes a rift with Yomi, leading to a mysterious disappearance. Meanwhile, the enigmatic Black★Rock Shooter and the Dead Master engage in a parallel struggle, mirroring the complexities of Mato and Yomi's relationship. As their fates intertwine, the truth behind Yomi's vanishing act and the significance of the blue star charm come to light.