The Holy Clavis (in Japanese: ホリー クレービス, Horii Kureebisu), also sometimes known as the "Clavis" (in Japanese: クレービス, Kureebisu), is a legendary artifact with dangerous mystical powers and an item in Lightning Returns: Final Fantasy XIII. This mythical and mysterious golden treasure chest-like relic is essential to the performance of the Soulsong. For this reason, it is desired by the powerful religious society known as the Order of Salvation as the important part of their ceremony in the name of their God, as well as Oerba Yun Fang, who is determined to find and destroy the Clavis before the Order can get their hands on it. To this end, Fang traveled to the Dead Dunes, where the object is said to be found, and founded the gang of desert bandits called Monoculus.
This legendary relic is, according to legends, said to have been made by the gods themselves. It is used in rites to summon the souls of the deceased.
It is believed that the Clavis lies somewhere within the ruins of the Dead Dunes, and the bandit gang Monoculus had their sights set on it for many years. The Order of Salvation, however, also shows a great deal of interest in the treasure, suggesting that it is no mere fairy tale, but a credible artifact from the past.
Both groups have searched the desert for the Clavis, but have been stymied by powerful seals that keep them out of certain ruins.
13 years before Lightning awakens from her crystal sleep, Oerba Yun Fang and Oerba Dia Vanille awoke from their own in the city of Luxerion, under the care of the Order of Salvation. When the Order discovered Vanille's ability to hear the voices of the dead, they became interested in her and placed her under their protection within the cathedral as their 'saint'. Then the Order came to seek the Holy Clavis, an ancient relic with the power to summon the spirits of the dead. It is called "holy" because many people including the Order of Salvation believed that this object is of heavenly origin. Fang learned the Soulsong will kill Vanille if she carries out the ritual, and ventured off to the Dead Dunes in hopes of finding and destroying the clavis to save Vanille.
When Lightning arrives to the Dead Dunes and vanquishes the sandstorm known as "God's Wrath" for Adonis, a member of the bandit gang Monoculus, she is granted an audience with his boss, who turns out to be Fang. Fang explains she is seeking the Holy Clavis and after witnessing Lightning's powers as the savior, believes the relic is finally within her grasp. Fang and Lightning team up to find the Clavis before the Order and they depart for the ruins.
After searching the ruins, Fang and Lightning unlock the sealed chamber containing the clavis. When the duo come before the legendary artifact, Fang comments on a strange force pushing down on her chest. From the Ark, Hope Estheim tells Lightning the Clavis was made either by humans with divine help or by the gods themselves. He alerts her to the approach of the Order's Secutors. Fang attempts to destroy the Clavis, but Lightning stops her, only to learn what will become of Vanille if she uses the device. The Secutors arrive in the chamber and Fang attempts to destroy the Clavis again against Lightning's wishes. Thanking the two warriors for their valiant efforts on behalf of "the sacred one," the lead Secutor summons the Grendel/Parandus for Lightning and Fang to battle as a distraction while his men get the Clavis.
When the Grendel/Parandus is defeated, Lightning and Fang discover the Secutors have taken the Holy Clavis. Fang reveals the Clavis' true nature as a tool for destroying the souls of the dead, as well as the reason why she desired it in the first place: to keep it from Vanille, rather than to give it to her as Lightning believed. Fang states the only reason she teamed up with Lightning was to ensure she did not hand the Clavis over to the Order herself, and Lumina appears, revealing it was her who tipped off the Secutors regarding the location of the Holy Clavis. Lumina shows interest in the Soulsong and how the Holy Clavis will destroy every soul trapped in the dark energy Chaos, including Serah's. Lightning demands to know when the Soulsong will take place, and Lumina tells her it will be on Nova Chrysalia's final day.
On the final day, Lightning travels directly to the Order's cathedral in Luxerion to stop the Soulsong and save Vanille and the souls of the dead as many of the city's citizens arrived at the cathedral with the Order of Salvation and prayed. She teams up with Fang and when the two reach Vanille's location, they find that she has begun the ritual due to the fact that Vanille is chosen as "The Savior" because of her special ability to hear the voices of the dead. As the souls are summoned to the Clavis, Lightning and Fang tell Vanille the truth about the Order and the Soulsong. Lightning tells her she has the power to lead the souls of the dead to the Ark to be reborn in the new world. Vanille agrees to stop the Soulsong, angering the Order's High Priestess, and a blast of energy from the Holy Clavis symbolically strips Vanille of her sainthood and casts her out of God's favor. As Vanille's life, it shines with a radiant light possessing the power to destroy the souls, but Snow Villiers arrives and uses Fang's Bladed Lance to destroy the divine relic and kill the High Priestess and soon her high-ranking followers within the Order in a radiant energy blast.
- The Holy Clavis' name comes from the word "clavis" which is a key or glossary serving as an aid to interpretation.