Kekkaishi, Vol. 10 (Kekkaishi #10)

By night, teenager Yoshimori Sumimura is a "kekkaishi"--a demon-hunter who specializes in creating magical barriers around his prey. By day, Yoshimori's got other demons to battle: an addiction to sweets and a seriously crotchety grandfather! Yoshimori's pretty neighbor and childhood friend, Tokine Yukimura, is also a kekkaishi, but their families are feuding over who is the true practitioner of the art.

The Kokuboro ayakashi launch a major assault on the Karasumori site to siphon its magical energies to heal their ailing princess. When our friends' mysterious new ally Gen pulls out every last stop to battle them, they make him an offer he can't refuse--join their demon alliance or perish!