Karasumori Academy was rumored to have been built on top of the ancient Karasumori site, where an underground mass of spiritual energy constantly attracted Ayakashi. Once Ayakashi enter the site, they are able to absorb the spiritual energy, becoming stronger and, more often than not, even more dangerous. This process may take anywhere from mere moments to a whole day, depending on various conditions. Kekkaishi have protected the site for generations, with the duty currently falling to Tokine Yukimura and Yoshimori Sumimura. They protect against supernatural threats, especially Ayakashi, either destroying or driving them away before they can tap into the site's boundless power and transform. In order to prevent innocents from being harmed, it is a school rule that no one be on the grounds