Blood limit. This term is used in the anime Naruto to describe the abilities used by a specific clan that can only be used by those born with specific blood line.
Yoshimori and Tokine are just your average kids who go to the same school together and they also happen to be neighbors. During the day they go their separate ways, but at night they both have to go protect the land of Karosumari. A job passed down to them from generations of Kekkaishi in both of their families. The families are 'rivaling' but the two of them get along just fine. At night Yoshimori and Tokine with their demon dogs Hakubi and Madarao, do their best to rid the land of evil. But everything isn't always so simple.