Onmyou Taisenki

Onmyou Taisenki (陰陽大戦記) is a Japanese manga series scripted by Yoshihiko Tomizawa and illustrated by Hiroyuki Kaidō. It was adapted into an anime series produced by Sunrise from September 30, 2004 to September 29, 2005.

Plot
All his life, Riku Tachibana has been raised by his grandfather. For some reason, the old man has always been fond of strange hand gestures, and they've rubbed off on Riku, who performs them almost subconsciously, to his classmates' great amusement. One day, however, it suddenly becomes clear to Riku what his grandfather has been surreptitiously teaching him. And the teachings could mean the difference between life and death for Riku.