Оотомо Джін

Harutora's homeroom teacher. A fairly quirky fellow who tends be more laid back then one would expect from a teacher, to the point where some would accuse him of being irresponsible. Despite that, he's usually good at giving solid advice to students and is known activist against the school's harsh policies when comes to education. He lost his leg in a clash with Ashiya Douman and now has a prosthetic leg. He was a former Magic Investigator and Divine General nicknamed "The Shadow" who worked under Daizen Amami to investigate the Twin Horn Syndicate until he gave his resignation and started working as a homeroom teacher of Onmyo Preparatory School in order to observe and protect Natsume.

(Source: Wikipedia)