Kidō (鬼道, "demon way" or "spirit way") is a form of Shinigami combat that is based on advanced spells produced with strong Reiryoku and fall into two categories: Hadō for direct offensive attacks, and Bakudō for means of battle support. It is one of the techniques in the Zannkensoki, the group of Shinigami primary combat skills. Kidō spells are triggered by an incantation, but experienced users can trigger them without an incantation, though the effectiveness of the spell will drop.
There is a branch of Soul Society's military which excels in the mastery of Kidō called the Kidō Corps that can be said a little hideous due to its members' secretive uniforms. There are also Noble Families that excel in Kidō like the Tsubaki Family, and Yamada Family.
Each Kidō spell is graded on a scale from 1 to 100, the latter being the most powerful and the most difficult to perform. The scale is also a measure of difficulty. To use Kidō, the Shinigami must recite the specific incantation for the spell, which is often long and requires a few seconds to speak.
The power of a spell relies on the power of the user instead on the usual saying that the power of one is based on its level, as even a low-level spell can be utterly devastating when utilized by a high-class Shinigami.
Sometimes, Kidō can also be used for everyday purposes as well like lighting a dark hallway if the spell is tweaked in the right way, with less power, as demonstrated by Jairez Tsubaki. Since Communication and Tracking fall into the category of Bakudō, spells that relate to them may be used for practical use.
There are three main types of Kidō: binding spells, destruction spells, and healing spells.
- Bakudō (縛道, "Way of Binding"): Spells that can immobilize an enemy or have an effect besides a direct strike. They may seem subtle, but such spells can give their users a tactical advantage when used properly. This is a broad category of mostly defensive spells which block/repel attacks, freezes enemies in place, or protects their users. It includes communication, absorption, and tracking. This class of spells also include Barriers and Seals.
- Barriers: Focused spiritual energy of a Shinigami formed into a solid form of energy. This energy can take on many shapes or colors as determined by the user. Barriers are said to be protective in nature and can be as simple as barrier only protecting one direction or encompass all sides of an area. Barriers are also used for containment while some barriers can be used offensively and for healing reasons. Some Barriers are created to mask spiritual pressure and can make one spiritually and physically invisible. Like usual Kidō spells, the strength of a barrier depends on the power of the user, as weak barriers are easily breakable while strong ones can last centuries. Barriers created by noble blood are said to be unbreakable by those of lesser status. Certain barriers can be placed beforehand and activated later, while others require certain artifacts and time to activate. Shinigami more experienced to the use of barriers can place barriers faster and stronger without the use of artifacts or incantations and the only known type of barrier for the use is defensive.
- Seals: They are similar to barriers, but are far more powerful and require far more preparation to create. Seals are only possible to use by those of sufficient spiritual power being that are meant to hold the most powerful or dangerous artifacts or beings. Seals are commonly hard to break. Most Seals are placed in the 90+ level scale of Bakudō as they can be destructive in nature around their users.
- Hadō (破道, lit. "Way of Destruction"): Is a category of most offensive spells that inflict direct damage to the enemy. Their effectiveness differs depending on the user. It is said that the effectiveness of the higher-ranked spells are beyond imagination. Most are said to be stronger with the use of incantations, but more experienced practitioners can do it without incantations.
- Healing spells: These spells do not have known names, numbers, or incantations to cast, and simply heal the target. As the user holds his/her hands above the patient's wounds, his/her palms glow with green spiritual energy to facilitate healing. When one heals with regular healing Kidō, they perform Reiatsu restoration first. By doing so, one can attempt to recover the physical body using the patients restored reiatsu and the healers external reiatsu. Therefore restoring the reiatsu when the physical body is in a fully healed state is no trouble at all.
A form of classification for Kidō spells that are considered illegal by the Soul Society. The use of such spells will commonly result in some form of lengthy imprisonment or worse. The Kidō spells that fall under this class are those that involve the manipulation of space and time and Kidō that sacrifices the self. It is also illegal to use such Kidō spells that may harm innocent citizens near the caster.
- Eishōhaki (詠唱破棄, "Incantation Abandonment"): a class of Kidō Incantation where the Kidō practitioner forgoes using a spoken incantation at all. While it decreases the time needed to release the Kidō, it drastically weakens the spell. While anyone well versed in Kidō can use this technique, it is most effective when done by a skilled practitioner, otherwise the spell could utterly fail (i.e.: the spell explodes in the user's face). The most skilled experts are capable of using this technique to amazing effect.
- Nijū Eishō (二重詠唱, "Twofold Incantation"): a class of Kidō Incantation where the Kidō practitioner mixes the incantations of two entirely separate Kidō spells together to save time and confuse ones' opponent at the same time.
- Kōjutsu Eishō (後述詠唱, "Spoken-After Incantation"): a class of Kidō Incantation where the incantation is recited after initiating the spell in order to power it up. So far, only
Kidō is commonly seen used in instances of surprise attacks, rather than all-out assaults, being most effective when one's opponent doesn't see it coming. Kidō is also usable with just the spell name and no incantation or spell number.