‘Nabari No Ou’

Rokujou Miharu was a seemly reluctant junior high student living in his own world. However, within him, lurked the ultimate power of Nabari, “Omnipotent”. To possess such supreme weapon, the Wolf Pack of Iga swore to bring Miharu back to Iga village. On the other hand, Miharu’s English teacher, Kumohira sensei, and classmate, Kouichi, were the Banten ninjas whose mission was to protect Miharu. A war waged over the ownership of “Omnipotent” thus started. To survive, Miharu must enter the hidden world Nabari, to become the king.

Descriptions taken from AniDB.net