Ninpo

Ninpo is a collection of techniques practiced by modern ninja for improving and protecting the mind and spirit, in contrast to ninjutsu, which is primarily concerned with the physical realm. Ninpo is the spiritual side to ninjutsu

Ninpo was the featured martial art in the horror/fantasy anime, "X". Ninpo has seen references in such films and books along this Japanese vein; one American example being John Allen's "REALM" series, where the main character, Timothy Barnhill, is attuned in the art of metaphysical discipline.