Natsume Tomoharu, an average high school student, carries a unique burden - the spectral presence of his late friend, Misao. Upon settling into his sibling's former residence, Tomoharu's routine existence is disrupted when he stumbles upon a cryptic locked briefcase. Despite the absence of guidance, he initially considers stashing it away. Yet, the tranquility of his home is shattered as various factions converge, all coveting the enigmatic case. Ignorant of its significance, Tomoharu and Misao find themselves entangled in a frantic bid to safeguard it. As they unravel the mystery shrouding the briefcase, its ties to Misao, and its world-altering potential, Tomoharu delves into a web of secrets and revelations.