Despite being just an ordinary high school student, Natsume Tomoharu is haunted by the ghost of his deceased best friend, Misao. His life takes a sudden turn when he moves in with his brother and becomes the unexpected owner of a locked and enigmatic briefcase. Intent on keeping it hidden, he soon discovers that several groups are hot on his heels, determined to obtain the case at any cost. With Misao's guidance, he manages to escape with the briefcase, but the mystery surrounding it only deepens. As Tomoharu delves deeper into the case's connection to Misao, he uncovers its awe-inspiring power, capable of changing the fate of the world itself. Driven by his insatiable curiosity, he vows to unravel the secrets surrounding the enigmatic object and unlock its full potential.