Spirit Arts

Spirit Arts (精霊術, Seirei-jutsu) are techniques, which manipulate odo to impart one's will and desired image onto mana, causing phenomena that alters the world around the user. The reason why this happens is because mana itself has a vague sense of consciousness.

Summary
In the Seirei no Tami, the Spirit folk, who have a deeper connection to Spirits compared to Humans, practices Spirit Arts rather than magic to cause phenomena. Ursula, one of the three elders explained that using Spirit Arts requires one to manipulate their odo (life energy), or what Humans refer to as magic essence and imprints their mental image on the mana, which overflows in the world, resulting in various phenomena.

But, in the Yagumo Region, their residents used Spirit Arts rather than using Magic, being a common thing among their people compared to other places because of Ryuo, who taught it to those who couldn't use it.

Spirits
Spirits are being's made of mana that, under miraculous circumstances, were able to develop their own consciousness. Spirits often materializes in a wide arrange of forms to interact with others, most of them being animals and being separated into different classes ranging from Low, Middle, and High-Class. They are noted as having extraordinary affinity for using Spirit Arts, in comparison to Spirit folk and Humans, befitting a technique meant to manipulate mana itself.

It is important to form contracts with Spirits, but this tends to be based on their own will. Once completed, Spirits tends to reside within their owner's body in spirit form, and materialize outside. For Spirits, their contractee acts as a source of odo, being the most comfortable for them to reside within. Because of this, a contractee and Spirit can communicate with one another via a telepathic connection between them. In addition to this, forming a contact with a Spirit allows Spirit Arts users to utilize it to a different level compared to before, and of course a magnitude over than magic.

However, different from Animal-Type Spirits, Humanoid-Type Spirits, who're considered the Highest Spirit Class can such as the Great Dryas are able to communicate with others and hold proper conversations. However, in comparison to others, Humanoid Spirits are extremely rare to the point of counting their numbers using one hand.

There are two different kinds of bonds formed between a Contractee and their Spirit. The first and basis one, being the Spirit Contract (精霊契約, Seirei Keiyaku) formed between them, which allows both parties to communicate easier. However, a secret technique created almost a thousand years prior by the Seven Wise Gods, Spirit Pact (精霊霊約, Seirei Reiyaku), where the Contractee and Spirit forms a much deeper bond, to where it is possible for it to be assimilated into their partner. At this point, it's possible for the Spirit to remake their contactee's body to resemble a Spirits, letting them change their soul into a weapon or armor, like the Spirit Equipment.

versus Magic
Spirit Arts is more difficult to learn compared to Magic, requiring one to detect, perceive, odo, and detect mana. It is far different from Magic, which require one to detect magical power (odo), and undergo a Contract Ceremony, which engraves a formulae in their body, turning it into an artifact. In other words, turning a natural being into an unnatural one, letting one cause certain set phenomena using chants and spells. Magic is much more easier to learn for Humans who has lower affinities for Spirits Arts.

Though difficult to learn, Spirit Arts allows one to cause more phenomena compared to those who uses magic, in addition to being possible without chanting and creating magic circles. These phenomena can also be controlled much freer than those using magic depending on the Spirit Art user's capabilities. To use Spirit Arts, one must not have a formulae engraved inside them and can form contracts with Spirits, natural beings born from mana who resides inside their host without turning them into an unnatural being.

Trivia

 * Rio speculates that the Heroes uses some form of Spirit Arts, because their Divine Arms are activated without magic circles and no incantations, aside from making the stronger image. Gustave, however, claims that they're special-type magic weapons usable to their assigned Hero.
 * One key difference is that the Heroes' methods with Spirit Arts, is that Spirit Art users feeds their Ode to Spirits, while the Heroes feeds it to their weapon. It was soon revealed that the Six Great Spirits were sealed in the Divine Weapons, making Rio's previous speculation close.
 * It's different than a magic weapon that can only activate the magic that been inscribed into it.
 * A singular type of Sprit Arts is referred to as "Spirit Art". However, when talking about Spirit Arts as a whole, the plural version is used.