Celestial Spirit King

The Celestial Spirit King (星霊王 Seireiō) is the ruler of the Celestial Spirit World and its inhabitants. He can only be summoned by a Celestial Spirit Mage sacrificing one of their Golden Keys, breaking their contract with that Celestial Spirit.

Appearance
The King is a gigantic Celestial Spirit. His most striking features are his very long white whiskers, blue skin and red eyes deprived of pupils.

He appears dressed in full plate armor in the color of turquoise and gold, the helmet on his head has the same colors, with the peacock feather on the top and adorned with horn-like features on its sides. Inherent in King's outfit is white cape, which has a habit of fluttering, even when the wind doesn't blow.

Personality
The Celestial Spirit King firmly believes in the established principles and rules of the Celestial Spirit World, and follows his duty to uphold them even when doing so "pains his heart", as it was the case when preventing Leo from returning home due to him breaking the only ironclad rule the King could not change, causing the death of his summoner. He, however, is not devoid of heart, and can empathize with the situations of his subjects, sometimes altering his original judgement: moved by Lucy's efforts to save Leo's life and by her resolve, the King realized the one at fault might be the rule, and proceeded to make an exception to it, allowing the Celestial Spirit to return to his world, and thus letting him continue living. When the time calls for it, he can be extremely cheerful and fun-loving, inviting Lucy Heartfilia and her friends to the Celestial Spirit World with a fake excuse to have a grand party and celebrate their return from Tenrou Island. He is quick to extend his friendship to both people and fellow Celestial Spirits, affectionately referring to them as "old friends", even after a single meeting, and places great value in those he has come to care for, claiming he will never forgive those who hurt them. He appears to have a penchant for reminiscing the old times, exchanging words about the past with Mard Geer before engaging him in battle.

Loke arc
The Celestial Spirit King appears when Lucy tries to open Loke's gate as she states she will change the law of the Spirit World. The King refers to Loke as his old friend and voices his crime. He says it doesn’t matter if the fault is direct or indirect, he still cannot return to the Celestial Spirit World. Lucy then interferes stating that Loke has been suffering for his friend's sake for three years. She continues yelling at the King and declares she won't accept anything but his innocence. At this point, Loke shouts that he wants to repent, but Lucy yells that he can’t since his death will bring more sadness, and will not bring Karen back. Using all of her strength, she summons all of her Spirits at once, an action which would have killed any other Celestial Spirit Mage. She, however, cannot hold them for long and says that her friends want him there. Loke tells her not to do this, as he doesn't want her to follow Karen's footsteps. At this moment, the Spirit King concludes that maybe the law is in error. He also realizes Loke betrayed Karen to protect Aries, and Lucy did the same thing to protect Loke. The King states he does not want this bond to be broken, so he makes an exception for this time and grants Loke permission to return to the Spirit World. The King lastly says that if Leo wants to repent, he should live on and protect Lucy, as he believes her to be a friend of such worth.

Grand Magic Games arc
Team Natsu with Wendy, Carla, Juvia and Levy are welcomed by the Celestial Spirit King whose appearance surprises everyone (except Lucy and Erza). Lucy steps forward and asks him about the crisis that Virgo told them about, but the Celestial Spirit King chuckles and welcomes the group back from their seven years sleep, announcing the start of the party, which leaves the group dumbfounded. The Celestial Spirits then reveals that the crisis was all a ruse so they could bring everybody to the Celestial Spirit World to celebrate, since Lucy would not be able to summon all her Spirits to Earth Land. Everybody then parties and celebrates together. During the party, the King tells Lucy and Gray their group is the first group of humans to ever visit the Celestial Spirit World. After the celebration, all Lucy's Spirits, including the King wish Lucy good luck, and then leave.

Tartarus arc
The Celestial Spirit King is later summoned directly to Earth Land during Fairy Tail's war against the Dark Guild Tartarus when Lucy, in a desperate effort, sacrifices the Zodiac key that allowed her to summon Aquarius, who urged her to do so after explaining how to call forth the King himself. Hurtling towards Cube from the sky, the Celestial Spirit King is able to easily tear the floating island to pieces with a swing of his sword, destroying the Demons' base. After the now lifeless wreckage falls to the earth, much to the shock of those inside, he descends to the ground to confront Mard Geer, identifying the King of Hades from a previous meeting.

Looking down towards Mard's hands, the Celestial Spirit King realizes that the former still carries with him E.N.D.'s book, only to be informed that noted book is the soul of E.N.D., Tartarus itself. The Spirit King then questions Mard's scheme, with the Etherious promptly revealing their plan to revive their guild master and return to Zeref. The Spirit King turns his gaze towards the wounded Lucy, asking if such reason is why she lies fallen and with tears running down her cheeks. Mard replies affirmatively, telling the Spirit King that this shall be their final confrontation. Lifting his sword upwards, the Spirit King announces that he will destroy Lucy's enemies, swearing upon their contract together that he shall never forgive them. The Spirit King swings his sword, creating large explosions upon contact with the ground. However, Mard easily dodges his every move and in turn uses Thorn Curse[his Curse to simultaneously counter-attack. Albeit, revealing yet another ability of his, the Spirit King unleashes his Meteor Blade, which creates a sizable crater within its path and destroys all of the thorns created by Mard, who yet again dodges the attack with ease.

As he fights the Underworld King, the Spirit King becomes aware of Lucy's distress—granting her Aquarius' power and telepathically asking her to rise to her feet, and let the stars guide her to victory. Before long, however, the King's movements begin to grow sluggish, as noted by Mard, and in a last-ditch effort to defeat the Underworld King, the King raises his sword into the air and chants, allowing him to cast Galaxia Blade, which, contrary to Mard's belief, is not a full-frontal assault, but a spell that dispels and erodes away at dark enchantments.Having freed all those caught in the clutches of Alegria and momentarily petrified Mard with his last technique, the King returns to the Celestial Spirit World, deciding to leave it up to Fairy Tail to defeat Tartarus.

Magic and Abilities
Sword Magic (剣の魔法 Ken no Mahō): Described by Lucy as the strongest among the Celestial Spirits, the Celestial Spirit King's fighting style revolves around the use of the sword he wields while summoned to battle, employing which he has proven himself capable of performing exceedingly destructive magical attacks, generating titanic blasts which can alter the landscape completely. His powers, however, aren't apparently limited to offense, allowing him to perform more subtle actions, such as dispelling Magic and petrifying those responsible for performing it.
 * Meteor Blade (メテオ ブレイド Meteo Bureido): An immensely powerful offensive technique which the Celestial Spirit King performs by putting both hands on his swords' hilt and then executing a vertical frontal slash with it. This motion causes a huge, linear blast to be generated in front of him, surging up to the sky in height and covering an incredibly long area (seemingly several kilometers) while causing astounding damage, capable of drastically changing the appearance of its elongated point of impact. The King first employed this technique during his battle with Mard Geer, but it was ineffective in striking him, with the Tartarus member remaining unharmed some meters away from the huge crater generated by Meteor Blade.
 * Galaxia Blade (ギャラクシア ブレイド Gyarakushia Bureido): A technique which the King employs by pointing his sword, held with both hands, towards the sky and then chanting out an incantation, causing the clouds to tear open to engulf the targeted area with a mastodontic, circular pillar of light, intense enough to have Mard Geer shield his face. Mistaken for a full frontal attack by the Tartarus member, Galaxia Blade isn't an offensive move: described as "a pure offering which erodes away the darkness", its power is to dispel spells which are foul in nature (quite possibly Curses), managing to undo Alegria's effects completely, and thus freeing the Fairy Tail members who had been absorbed by it. In addition, this move was shown encasing in stone Mard Geer, the one responsible for casting the dispelled Curse, for a limited amount of time, momentarily removing him from battle.

Telepathy (念話, テレパシー Terepashī): The Celestial Spirit King was shown communicating mentally with Lucy from afar, announcing that he would lend her Aquarius' power and encouraging her to fight Jackal. It's unknown whether his telepathic powers are limited to communicating with Celestial Spirit Mages.

Celestial Spirit Powers: Ruling over both Celestial Spirits and their world, the Celestial Spirit King possesses a number of special abilities, some of which are common to his fellow Spirits, while others are seemingly exclusive traits of him.
 * Immortality: As a Celestial Spirit, the Celestial Spirit King cannot die, unless he is somehow forced to stay in the human world; an instance which, seeing as he's the one in charge of opening the gate to his dimension, seems remote.
 * Omniscience: The Celestial Spirit King appears to have a degree of insight of what is happening in Earth Land even when he is in the Celestial Spirit World, as shown from him appearing in the former place to uphold his world's rules when Lucy claimed she would have changed them.
 * Celestial Spirit World Gate: As the ruler of the Celestial Spirit World, the King is the one deciding whether to allow or not the return of Celestial Spirits to it; it was his will that eventually allowed Loke to return home after four years in Earth Land, saving his life.
 * Time Manipulation: The Celestial Spirit King has the ability to pause time indefinitely in selective locations upon apearing in Earth Land, as shown when he stopped the falling of Loke's glasses in mid air, at the same time letting time flow normally for him and Lucy.
 * Teleportation: Inside the Celestial Spirit World, the King is capable of teleporting both himself and nearby Spirits by raising his cape, disappearing into a puff of smoke to relocate elsewhere.
 * Empowerment: The Celestial Spirit King is able to bestow the power and abilities of a Celestial Spirit unto a human for a limited amount of time, even from a great distance away. This action grants them a boost to their Magic Power and gives them access to the abilities of said Celestial Spirit, which are shown to even be activated reflexively to protect the user from external harm. When doing so with Lucy, he gifted her with the powers of Aquarius, the Spirit whose Key she broke in order to summon him; it's currently unknown whether he can do so with a Spirit different from that "sacrificed" in his summoning as well. However, it appears using this power takes a toll on the King himself, making him considerably tired, with Mard noting how his movements had gotten "sluggish" following Lucy's empowerment.

Flight: The Celestial Spirit King is capable of keeping his huge figure suspended in the air at his will, whether hovering tens of meters above the ground or merely floating close to it, as well as to fly around at extreme speed, leaving behind a trail similar to a falling star's.

Immense Magic Power: A being reigning over an alternate dimension, the Celestial Spirit King possesses outstanding Magic Power. His appearance in Earth Land before Lucy and Loke caused the water from the nearby waterfalls to be entirely removed from its site, being lifted into the air to herald his appearance. He can release his Magic Power into a huge, potent shockwave, fitting his gigantic size; this drastically affects his surrounding area, and is strong enough to reduce rock into pieces.

Immense Durability: The Celestial Spirit King possesses inhuman durability and resilience, emerging completely unscathed from Mard's Thorns spell, which had him pierced from side to side by a multitude of massive thorns, many of which went through vital spots (namely his head and torso), showing only mild discomfort in doing so; he proceeded to counter-attack immediately afterwards, continuing the battle as if nothing happened. The King of Hades himself went on to remark on the feat with an admired expression.

Immense Strength: Fitting his gigantic size, the Celestial Spirit King is insanely strong, being capable of destroying Plutogrim, a being immense even for him, by propelling himself through it while slashing with his sword, splitting the flying structure in four pieces with a huge shockwave. He could also break all of the oversized thorns which Mard had sent piercing him and holding his body in place with a single movement.

Equipment
Sword: When summoned, the Celestial Spirit King carries with him a large sword, accompanying his large size. He is extremely skilled with the blade, as he was easily able to slice Cube into pieces, destroying Tartarus' floating base, Plutogrim.

Fairy Academy - Yankee-kun and Yankee-chan!
Celestial Spirit King appeared in the Fairy OVA: Fairy Academy - Yankee-kun and Yankee-chan! as a bust with the Fairy Tail insignia on his stand in front of Fairy Academy.

Quotes

 * (To Loke about Lucy Heartfilia) "Even after this, if you still feel compelled to atone for your sin, then I command you to become a pillar for your friend and live on. Those are the type of friends who have the most significance. There is much nobility in being willing to lay it all on the line to protect someone."
 * (To Team Natsu) "May the divine protection of the stars watch over you!"
 * (To Mard Geer) "I swear upon my old friend's determination and our contract together, I will destroy her enemies!"

Battles & Events

 * Lucy Heartfilia (summoner) vs. Tartarus
 * Leo's Return