Ragnarok the beast shall bring down Cocoon. After the War of Transgression, two girls from the far north shall come to Cocoon, the nest of Lindzei, and transform into the beast that destroys it. Until the end of time, this day shall be known as the Day of Ragnarok.
Catastrophe (カタストロフィ, Katasutorofi?), also known as the Day of Ragnarok (ラグナロクの日, Ragunaroku no Hi?) from 0 AF onwards, is an important event at the end of Final Fantasy XIII, and is a key event in its sequel, Final Fantasy XIII-2.
Three years ago, mankind stared into the face of extinction when Cocoon almost crashed onto the surface of Pulse.
The sphere's fall was halted by Lightning's companions, Fang and Vanille. Their desperate sacrifice summoned a massive pillar that cradled the plummeting Cocoon in its crystalline branches, averting an unimaginable disaster. The two l'Cie now sleep within the pillar in crystal form, and there are some who believe Lightning slumbers alongside them.
A new age began from that day forth, with each subsequent year marked by the letters AF, or 'After the Fall.'
When Lightning, Sazh Katzroy, Snow Villiers, Hope Estheim, Oerba Dia Vanille, and Oerba Yun Fang defeat Orphan in its true form, Eden loses its power source and the Cocoon fal'Cie shut down. Cocoon begins to descend but Vanille and Fang become Ragnarok to prevent Cocoon from crashing onto Pulse, encasing the sphere in crystal and forming a crystal pillar between it and Gran Pulse.
Their action, technically fulfilling their Focus, crystallizes the pair within the pillar's core while the others are crystallized on the Archylte Steppe. As revealed in Final Fantasy XIII-2, goddess Etro bore witness to the Catastrophe and took pity on Lightning's group, restoring not only them but her sister Serah Farron and Sazh's son Dajh Katzroy as well. After giving her blessing to Serah and Snow's marriage, Lightning was the first of many to suffer the consequences of Etro's intervention.
The event is described in detail from the point of view of a regular citizen getting caught up in the events in Final Fantasy XIII Gaiden Shōsetsu: Yumemiru Mayu, Akatsuki ni Otsu. Antimatter Manipulation Principle technology plays a big role in saving the citizens of Cocoon during the Catastrophe, as a girl named René well-versed in the technology hacks Cocoon's systems to stabilize its internal gravity during the fall, and the populace takes shelter in the cities' evacuation areas that escape the adverse effects of Cocoon's acceleration with the AMP tech at its maximum output. However, in parts of the cities not subjected to gravitational control, buildings crumble, roads ripple, seas gush, and mountains come apart and fall towards the sky.
As Etro released the l'Cie from crystal stasis chaos from Valhalla flooded into Gran Pulse. Sucked into the Unseen Realm with most of the chaos, the rest seeping in the land's soil, Lightning was removed from that point in time. All but Serah believe Lightning to have died or sacrificed herself alongside Fang and Vanille.
The event caused a time disturbance that claimed the life of Paddra Nsu-Yeul and her various incarnations, causing her Guardian, Caius Ballad, to embark on a quest to destroy both Etro and reality itself. Fang and Vanille continue their role as Cocoon's pillar for 500 years until being safely removed prior to the structure's destruction due to erosion of the pillar's crystal over the centuries.
Another side effect of Etro's intervention caused two hours to disappear from the length of a day, reducing it from a twenty-six-hour day to a twenty-four-hour day.
A catastrophe is "an event causing great and often sudden damage or suffering."
Ragnarök is an event in Norse mythology that is similar to the Apocalypse. It is an event that is set off by the death of the god Balder, which was orchestrated by Loki. The Ragnarok was a final clash of all the major entities of Norse mythology. This caused all of the human spirits up in Valhalla to come down for the final battle.
This bloody encounter ebbs with the destruction of the universe and Balder along with a little handful of entities that are put in the bodies of children and only contain memories of the world before Ragnarok. Those entities would become mortal, and would live again in a new world of plenty and just existence.