The adorable shrine maiden Fuzuki Kanon has at last been summoned, and she brings with her hope that the demon lord will finally be eradicated. However, when agents of Lapter sneak into the castle in an attempted assassination, the sealing stone breaks! And since Rosemary is the closest person to the stone when it happens, she becomes the prime suspect for the demon lord's possessed vessel. Meanwhile, Nevel begins their counterattack on Lapter, shattering the peace that the world has enjoyed for so long. To make matters worse, Sir Leonhart has grown distant, occupied by his knightly duties. Countering Lapter's skullduggery, pinning down the demon lord, and getting through to Sir Leonhart—can Rosemary resolve all these issues before she's married off to another country's prince?