Onmyou Taisenki(2004)

Onmyou Taisenki is an anime series following Riku Tachibana, a boy raised by his grandfather who has unknowingly learned mysterious hand gestures throughout his childhood. When Riku's classmates mock these strange movements, he dismisses them as harmless quirks. Everything changes when he discovers the gestures are actually powerful incantations tied to ancient magic. What seemed like innocent family tradition becomes a matter of survival as Riku realizes his grandfather has been training him in occult arts for a reason. Now caught between his ordinary school life and a hidden supernatural world, Riku must master these newfound abilities to face dangers he never knew existed.