Kaoruko Mochizuki runs an herb shop in a small seaside town. One day, a mysterious man dressed in black named Kaname Hibiki enters her shop and reveals that Kaoruko is actually a witch. And what's more, Kaoruko needs Kaname to help control her awakening power!

In order to become a Black Witch, Kaoruko makes a pledge with Kaname. However, that means that Kaname will be breaking his pledge as a knight and betraying the Witch Queen! If the Witch Queen awakens, Kaname will suffer a terrible punishment... Meanwhile, Kaoruko is being stalked by someone who is after her powers!