Essential to even the most basic shaman magic, Furyoku (巫力, Furyoku, "shamanic power"), called Mana in the English version of the Manga, is the measure of the sixth sense that an organism is born with. Generally a product of will-power, Furyoku can be generated either naturally or artificially (e.g. Golem). Furyoku's consistency is contingent upon the being's conviction. Every living thing (plants, animals, and human beings) is given a measure of Furyoku by the Great Spirit prior to birth to live out their lives, and upon their death, that power returns to the planet. During an organism's lifetime, their cumulative experiences form memories, which upon death return to the planet along with their Furyoku. These memories, in turn, give rise to more Furyoku, allowing the planet's spirit as a whole to grow, and the cycle of life to continue.
While predetermined upon birth, Furyoku can be increased. However, like the five basic senses (sight, hearing, touch, smell, taste), Furyoku is an inborn power that cannot be improved merely through physical training. The process for increasing a shaman's Furyoku usually involves a "pseudo-death" experience. Such ventures usually involve the shaman being stripped of their physical senses, leaving bare their sixth sense. Throughout the ordeal, the shaman must contend with the onslaught of negative emotion from his own being, relying only on his strength of heart to sustain them. After such an ordeal, the shaman's soul would be strengthened, if not broken to a degree that the shaman may never recover.
An alternative method of increasing Furyoku is actual, physical death and near-death. Whenever a shaman is mortally wounded and subsequently revived, their Furyoku increases dramatically. It is for this reason that the leader of the X-Laws, Jeanne spends her time in her iron maiden. Her Furyoku increases almost constantly, due to the torture she subjects herself to at all times.