Celestial Spirit

For the related Magic, see Celestial Spirit Magic.

Celestial Spirits (星霊 Seirei) ,are magical beings from their own separate universe, the Celestial Spirit World. Mages, called Celestial Spirit mages, are able to summon spirits by opening their gates through the use of Keys.

All Celestial Spirits are named after a different astronomical constellation.

Contracts and Rules
When a Celestial Spirit Mage receives a Key and opens its Celestial Gate for the first time, they have to set up a contract with the respective spirit. This contract consists of asking the spirit which days it can be summoned by the Mage. This simple agreement, much to the shock of Natsu and Happy, forms a dedicated, serious bond between the Spirit and summoner. However, under certain circumstances, i.e. during battle, a contract can be asked to be completed later. Contracts can be broken if the Mage gets arrested, releases the spirit by him/her self, or dies. When a Celestial Spirit Mage summons a spirit, it appears directly next to them, as that's where the gates to the Spirit world had been opened. It's impossible to summon spirits elsewhere. The spirits must also abide by certain rules enforced by the Celestial Spirit King. The only rule that has been introduced in Fairy Tail so far is that a spirit may not directly or indirectly kill its summoner under any circumstances.

When the gates are closed, it is required from both the summoner and the spirit to agree upon the gate's closure. However, spirits can also be "forced closed" in battle, which means they can be forced back into the Celestial World by the summoner's will, though not every Celestial Spirit Mage is capable of doing that.

Celestial Spirits also have different categories of sorts, that fall under the basic summoning conditions from their owner. For example, Loke summons himself most of the time without Lucy doing so herself, Virgo also has summoned herself once, as have Gemini and Horologium and if trust between the Celestial Spirit and the Owner is not an issue, contracts can be temporarily dissolved. It also seems that if the Celestial Spirit is strong enough, they can use their own Magic to stay in the Human World, when/if the contract is not in action. The strength of the Celestial Spirits is affected by the Magical strength of their summoner as Lucy once said that her spirits could become even stronger than Natsu if she trained more.

Types of Keys

 * Gold Keys: Gold Keys are one of a kind; being able to summon the strongest Celestial Spirits.
 * Silver Keys: Silver Keys can be bought anywhere, and are noted to be rather inferior to gold.
 * Crystal Keys: One of the most valuable types of keys. While they are not as powerful as Gold Keys, but they are stronger than silver keys, and crystal keys are easier to find than Gold Keys. It is said that like Gold Keys, Crystal Keys are one of a kind, but they are larger in quantity. In several cases, Crystal Keys are noted to surpass the power of Gold Key spirits on occasion.
 * Red Keys: A red key celestial spirit is a spirit who has been banished from the celestial spirit world for any number of reasons, they are noted to be extremely powerful, rivalling gold.
 * Lost Keys: Lost keys are very rare. They are black in color. Lost keys are Celestial Spirits that either have been forgotten or replaced.

Celestial World
All Celestial Spirits spend their time in the Celestial Spirit World when not called through by their summoners. Being in the World seems to have some sort of rejuvenating effect on the spirits, restoring their health after being in the human world which, over long periods of time, can potentially kill the spirit. The reverse is also possible: humans are unable to breathe in their World so after a period of time, albeit a much shorter one, they would die. Such an occurrence (a human entering the Celestial World) is a serious breach of contract. This rule, however, is not absolute, since Natsu survives an extremely brief period in the Celestial Spirit World when he catches hold of Virgo just as she transits through the spirit world to reappear elsewhere in the human world at Duke Everlue's command.