Mirai Kuriyama is the sole survivor of a fierce clan in the spirit realm that uses their own blood to vanquish personified negative emotions called "youmu." She encounters Akihito Kanbara, a hybrid of both human and youmu, while lost in thought on the rooftop of their school. In a failed attempt to kill Akihito using her blood saber, Mirai discovers his immortality, creating a peculiar bond between them. While still determined to defeat Akihito to prove her worth as a fighter in the Spirit World, Mirai and Akihito join the Literary Club and team up with skilled warriors Hiroomi and Mitsuki Nase to battle stronger youmu threats. Their ultimate goal is to defeat the most menacing youmu, Beyond the Boundary, to survive.