Ragnarok (Final Fantasy XIII)

Ragnarok is a non-summonable Eidolon in Final Fantasy XIII. It is the legendary beast that a l'Cie must transform into in order to bring about the obliteration of Cocoon.

Fated Beast
The fal'Cie of both Cocoon Pulse, desire for l'Cie to become Ragnarok and destroy Cocoon in order to bring back the "Maker," the deity that created the world. In order to bring back the god they yearned for, the fal'Cie realized that a ideal sacrifice needed to be made, namely the deaths of Cocoon's vast people. Though powerful. Cocoon fal'Cie are prohibited from attempting harm to Cocoon and so use humans as Pulse l'Cie to suit that end.

This in turn sparked the War of Transgressions, putting both humans on Cocoon and Pulse at odds with each other to ensure Ragnarok's coming. Oerba Dia Vanille and Fang were selected from the village of Oerba to become Ragnarok. But Vanille, frightened at the task of killing those of both Pulse and Cocoon, refused to transform into the beast; Fang attempted to replace her, but the resulting transformation was incomplete and failed. For reasons unknown, Vanille and Fang both crystallized; apparently the Pulse fal'Cie were pleased with their efforts, and Barthdelus took the Pulse Vestige to Cocoon where they would reawaken to finish the job.

Born Anew
Five hundred years later, Barthandelus had taken peaceful political rule over Cocoon as Primarch Galenth Dysley. After they awaken, Vanille remembers their previous Focus, but hides her knowledge, as Fang cannot recall anything of Ragnarok. Bearing the guilt of Ragnarok within her, Vanille simply goes along with Fang's attempts to revive "their" memories, attacking the Cocoon fal'Cie Kujata. The incident only served to separate the two, Vanille bearing her guilt and looking for a way to escape to Pulse, while Fang joins the Calvary under Cid Raines.

During the Purge, Vanille boards a train headed for Pulse, meeting Lightning, Hope, Snow, and Sazh after the incident at Hanging Edge flies out of control. The five are branded by the Anima, a Pulse fal'Cie that Barthandelus had hidden along with Vanille and Fang in the piece of Pulse Vestige left on Cocoon. Though tasked with yet another mission to bring about the end of Cocoon, Vanille continues to hide her knowledge of the past from her friends, keeping silent or playing innocent during her journey with Sazh, who harbors anti-Pulse feelings.

Fang, meanwhile, learns of the other l'Cie after helping to apprehend Snow, and reunites with Vanille and the others upon the Palamecia. There, they also meet Dysley, who reveals himself as Barthandelus and taunts Fang's inability to remember her fate. On Pulse, Fang gradually begins to recall her mission of the past and confronts Vanille, who admits she was hiding the secret so they would not have to transform into the beast again. Barthandelus appears to them once more as they scour the ruined city of Oerba, first taking the disguise of Serah Farron. Serah's shade chants to legend of Ragnarok, begging the party to open its eye to its inevitability, but they reject her, and Barthandelus reveals his true form in order to convince them by force. After his temporary defeat, Vanille, Fang, and the rest of the party resolve to save Cocoon rather than destroy it.

When the party passes through Edenhall and descends into Orphan's Cradle, Barthandelus orders them one last time to accept their destiny and kill Orphan and the whole of Cocoon. Vanille and Fang refuse, and Barthandelus decides to eliminate them and await new l'Cie. The protagonists prove stronger than he, and as the fal'Cie sinks into Orphan's pool as he is absorbed the awaken fal'Cie as sword-like shell for it to force a conversion into Ragnarok. After a lengthy battle, Fang begins to waver and decides to begin the transformation; the other party members save Vanille are transformed into Ci'eth. Vanille pleads with Fang to reject the fate of Ragnarok, but her words are in vain. Fang is only able to morph into an inferior version of the beast, unable to kill Orphan, who resorts to torturing a restored Fang to make her assume the intended form.

Just as Vanille seems ready to acquiesce, the other party members will themselves out of Ci'eth form and blast Orphan, causing its shell to crumble into its pool as Orphan rises in its true form. The party resolves to defeat Orphan without the aid of Ragnarok, killing it and causing it to explode, signaling the end of Cocoon.

Lightning, Snow, Sazh, and Hope rise out of Orphan's Cradle, floating up with scattered light, but Vanille and Fang choose to remain at Eden's core. As the other four drift safely away, the Oerbans transform into Ragnarok together as Cocoon descends like a meteor towards the volcanic land of Pulse below. With the strength of Ragnarok, Vanille and Fang freeze the lava and evoke a crystal pillar from it, enveloping and slowing Cocoon. Ragnarok supports the falling globe and emits a shower of crystal wind, causing the molten surface of Cocoon to freeze in a glass-like substance, balanced upon the crystal pillar. Lightning, Snow, Sazh, and Hope survive, their l'Cie marks erased; Cocoon's days of plenty have ended. As evacuees from Cocoon spread out amongst the land of Pulse, Vanille and Fang, crystallized in Cocoon's center, encourage the party to greet a new dawn.