According to the legend, five hundred years ago, there was an insignificant lord who possessed a mysterious power that drew ayakashi (妖?) (supernatural creatures) to him. A demon exterminator, Tokimori Hazama, was called upon to protect the lord and his castle. The lord's power stayed on the land even when he had died. Thus, Tokimori founded the Hazama clan, who inherited his techniques, to protect the land for centuries to come. This land is Karasumori (烏森?).
In the present day, Yoshimori Sumimura and Tokine Yukimura, heirs of the Hazama clan, are the kekkaishi (結界師?) that protect Karasumori. They are ability users (people who can use supernatural powers) who use a technique called Kekkai (結界?). Kekkai is a form of magical energy barrier which is primarily used to capture and destroy ayakashi that are drawn to this shin'yūchi (神佑地?, "sacred land"). Any ayakashi that stay on the land become stronger. Yoshimori and Tokine are to guard the land from the intrusion of ayakashi who try to "power-up" there.
