The Sword of Kings is a greatsword in Final Fantasy XII. It belonged to the Dynast King Raithwall and has the power to cut nethicite. It is obtained during the storyline after the plot events at Giruvegan and is treated as a key item which means it cannot be sold. As with the other key item greatsword Treaty-Blade, it does not require a license to equip and so can be equipped by anyone, and unlike standard greatswords offers no knockback. In the original version its stats are the same as the Treaty-Blade, however the Treaty-Blade is stronger in the Zodiac versions.
The Sword of Kings was given to King Raithwall centuries ago by the Occuria, self-appointed gods of Ivalice who wish to steer the land's history to a direction they deem appropriate by meddling with the mortals' affairs. The Sword of Kings was given to Raithwall so that he may cut off nethicite from the Sun-Cryst, a powerful crystal and the source of all nethicite power. He traveled to the Pharos and cut three shards off the Cryst, and wielded the nethicite to unite all of Ivalice in the Galtean Alliance. He gave the Sword of Kings to the Gran Kiltias of the Light of Kiltia faith to keep it safe. The Gran Kiltias did so, by sealing it in the Stilshrine of Miriam.
Seven centuries later, Princess Ashe arrives Mt Bur-Omisace looking for a power that can counter nethicite. A rogue Occurian Venat wants to undermine the other Occuria's influence in Ivalice by instating his own "Dynast-King," Vayne Carudas Solidor of the Archadian Empire, and has spurred the empire to steal the pieces of deifacted nethicite Raithwall once cut from the Sun-Cryst from the kingdoms of Ivalice, as well as taught the Archadian scientist Cidolfus Demen Bunansa how to manufacture manmade nethicite. Vayne and Venat's conquest of Ivalice threatens Princess Ashe's kingdom of Dalmasca, and Gran Kiltias Anastasis tells her of the Sword of Kings. The party travels to the shrine, and finds the sword.
Ashe's traveling companion Vaan urges Ashe to test the sword's might against the lusterless Dawn Shard, a piece of deifacted nethicite that has lost its power. Ashe attempts it but her hand is stayed by an apparition of her late husband, Lord Rasler. Rasler's ghostly visit convinces Ashe the sword is genuine, and the party heads for the Draklor Laboratory in Archades to destroy the empire's nethicite with it. They fail at their quest, as Cid escapes with the nethicite in hand.
Cid lures Ashe to the Ancient City of Giruvegan where she is spirited away to the realm of the Occuria, who wish to make her their new Dynast-King to oppose Venat and Vayne. The Occuria gift her the Treaty-Blade, a "sister sword" to the Sword of the Kings that likewise can cut though nethicite, and task her with carving her own pieces of deifacted nethicite from the Sun-Cryst to lay waste to the empire.
Upon reaching the Sun-Cryst Ashe must decide whether to destroy it, or use its power to defeat the empire like the Occuria ask her to. Upon realizing she has been manipulated by the Occuria to do their bidding via illusions of her late husband, she decides to destroy the Cryst and rid Ivalice of nethicite. Wielding the Sword of Kings and the Treaty Blade, Vaan and Ashe attempt to destroy the Cryst, but it has grown too volatile for them to get close, spilling Mist over Ivalice.
Reddas, a mysterious sky pirate traveling with Ashe, takes the Sword of Kings from her and destroys the Sun-Cryst while Ashe and the others escape. Reddas is killed in the explosion, and it can be assumed the Sword of Kings was destroyed along with him. With the Sun-Cryst destroyed nethicite loses its power, and the Occuria lose their means of manipulating human affairs to their own ends.