Tamaki Kasuga returns to her grandmother's mountain village expecting an ordinary stay, and instead inherits a duty passed down from her ancestor Princess Tamayori: to keep the sword Onikirimaru sealed. Because the Tamayori blood runs in her, only she can hold the seal, and five young men are bound to protect her, among them her classmate Takuma Onizaki and the group's leader Suguru Oomi. As Tamaki learns what her bloodline asks of her, the organization Logos moves against the seal she now guards.