Reiryoku (霊力; Japanese for spiritual power) is a set of supernatural abilities aligned with the spiritual sensitivity and energy of the user.
While all humans posses spiritual power from their souls; Shintō Kannushi (Priests) and Miko (priestesses), Buddhist monks and Nuns, Sages, Saints, Yamabushi, Exorcists (see Madame Exorcist) and other such Ascetics generally had more knowledge, training and understanding on how to exercise this power for specific purposes, having been trained to do so (usually from a young age). It is also known that the excessive usage of spiritual power can be extremely exhausting, and may place great strain on the user's body, causing them to experience symptoms of fatigue or even death.
Most yōkai are especially vulnerable to a human's spiritual power, primarily due to its nature of clashing with their demonic energy. However, some demons (e.g. the Miko fūji and Oni's head) are capable of absorbing spiritual power from monks and priestesses alike to fuel their own power. Daiyōkai, such as Kaguya, are even capable of utilizing this power for themselves, should they absorb it from an individual with great enough spiritual power.
- Onmyōdō (陰陽道; Japanese for ‘The Way of Yin and Yang’): There are several mystic spells and enchantments that are derived from spiritual energy. Most of these spells are used as attacks, defensive measures, or to bind others, and their potency is dependent on the extent of spell-caster's spiritual power. These spells, depending on their requirements, can be triggered by a ritual action, an incantation, a gesture or any combination of these. Some spells may require the use of paper charms or talismans, and other ingredients for various purposes.
- Enchantments: Those with tremendous spiritual power are able to enchant and craft objects of mystic power, like the Sacred Jewel. Midoriko, the jewel's creator, used the fabric of her own soul to capture and seal a demonic spirit inside of her body before expelling it along with her spirit, thus forming the Shikon Jewel. Such objects differ from items that might act merely as conduits for spiritual energy (e.g. Kikyō's bow or Miroku's staff), in that the object itself becomes a source of power independent of its creator. The cauldron designed by Lady Kanade which helped to protect Hōraijima is another example of a mystic object created by a powerful priestess.
- Curses: Spells such as these affect an object or person in a negative manner (i.e. remotely killing others or mind-control). This was demonstrated by the dark priestess Tsubaki when she cast a curse which killed an unnamed lord. With the Shikon no Tama, Tsubaki was also able to control Kagome and force her to attack Inuyasha.
- Sutras: Sutras are written incantations that act as an amulet or talisman of protection. Normally, they are written on paper charms, called o-fuda (御札 or お札), in order to ward against, reveal, bind, or punish otherworldly creatures (i.e. demons or spirits). Sutras can also used to erect physical spiritual barriers.
- Sealing: With great enough spiritual power, one can employ a combination of enchantments and barriers to bind a demonic being into a kind of spiritual prison. The ogre found in the Forbidden Tower who was released by Tsubaki is one such example of a demon being sealed behind a barrier of enchantments.
- Shikigami Conjuration: Spectral entities created and empowered by the creator's spiritual energies. Shikigami are capable of assuming a variety of different forms, from human to animal, and they act under the will of whoever summoned them. They are normally employed for tasks such as spying, stealing and enemy tracking. The dark priestess Tsubaki sent her spirit puppet to collect drops of Kagome's blood whereas Kikyō's shikigami gathered her items like a branch of ōkatama. These spirit puppets can also be used in far more offensive manners, such as to cause bodily harm or even death.
- Energy Projection/Manipulation: Spiritual energy itself can be manipulated and controlled for a variety of effects. Users can concentrate spiritual energy in the palms of their hands for offensive purposes or focus their spiritual power into energy shields or screens. The size, strength, and durability of an energy barrier is dependent on the one who erected it; the greater their spiritual power, the more resilient their barrier is. While barriers are protective in nature, they can be used for offensive purposes as well.
- Energy Infusion: Users can channel their spiritual energy into their weapons to empower and energize them (i.e. sacred arrows). This can greatly enhance the recipient object's qualities and efficiency.
- Purification Abilities: According to Lady Kanade, a human's spiritual power normally clashes with the demonic power of a demon. Thus, if the human's spiritual power is strong enough, they can dispel the infernal energy of a demonic force. Those with great spiritual power, like the priestess Kikyō or Kagome, can also resist and purify the effects of demonic miasmas by either consciously or unconsciously sending out pure spiritual power.
- Spiritual Awareness: Those with above average spiritual power seem to have an abnormal "sixth sense" that enables them to detect both barriers and demons alike, even when a nefarious being such as them is concealed by magic. Kikyō was able to detect Naraku's aura even after he had disguised himself as a feudal lord. Some spiritualists can even perceive things that are otherwise invisible to ordinary people (e.g. ghosts, spirits, and divine auras); this is referred to as "the sight."
- In the Manga and Anime; while the spiritual powers of Shintō Kannushi (Priests) and Miko (priestesses) is referred to as "Reiryoku"; the spiritual powers of Buddhist monks and Nuns are referred to as "Hōriki" (法力; Japanese for Dharma Power)); and the spiritual powers of Sages is referred to as "Senki" (仙気; Japanese for Sage/Hermit Spirit/Force)).
- While all humans have spiritual power, there are certain gifted individuals, like Kikyō and Hitomiko, who innately have a greater concentration of spiritual power. The exact source of innate spiritual power is not explicitly known.
- Kikyō and her sister Kaede had above average spiritual power, and Miroku's family was known to have monks with great spiritual power, suggesting a genetic link as an explanation for spiritual powers. Kikyō's genetic clone having had some level of spiritual power further reinforces this theory.
- However, as both Kikyō's and Kagome's spiritual power extended to the spiritual level, allowing the former to be reincarnated as the latter with the same innate spiritual powers, suggests an obvious accompanying spiritual connection for their unusual powers.
- According to Lady Kanade in InuYasha the Movie: Fire on the Mystic Island, the spiritual power a human possesses normally clashes with the demonic power of a demon, in half-demons this power merges and produces a unique synergy of these powers.
- As seen in the anime episode Koga's Bride-To-Be, certain plants, like the Iris flower, can possess spiritual power and purifying abilities.