Kekkaishi Graphic Novel Volume 31

Yoshimori is trapped in a formless void! The next day, the founding master of the kekkaishi himself appears at Yoshimori's home and offers to train him in a unique kekkai style. Is Yoshimori's visitor friend or foe? And why is he also offering to train the vicious Ogi heir, Shichiro...? Meanwhile, the witch Kakeru plans her revenge...