Resting in Cocoon's shadow, the sprawling and enigmatic lowerworld of Pulse is home to a multitude of terrors. The land is commonly believed to be inhospitable to human life, and a strict ban on interworld travel forbids citizens of Cocoon from venturing there to challenge this hypothesis. Not even members of the Sanctum's upper echelon can claim to have seen the surface with their own eyes, but the attempted invasion by the world's savage armies several centuries ago is well documented. Widespread fear of a repeated assault persists among the populace even today, with colloquial references often likening the world to a manner of living hell.
Fal'Cie are an existence beyond human comprehension, possessed of incredible magic power. The ones responsible for Cocoon's construction are protectors of humanity, but there are others of their kind as well: the fal'Cie who dwell on Pulse and name themselves enemies of Cocoon.
Humans who encounter Pulse fal'Cie are cursed, being turned to l'Cie and ordered to destroy Cocoon. It is for this reason that most ordinary citizens support the Purge - anyone who may have come into contact with one of these fal'Cie represents a dire threat.
The beings known as fal'Cie possess the power to enthrall unwilling human instruments, compelling the victims to serve their will. These individuals, known as l'Cie, are marked with indelible brands. They gain the gift of magic, but also bear the burden of completing a task known as a Focus for their fal'Cie master.
Pulse l'Cie - tools of fal'Cie from the world below - are considered dangerous enemies of Cocoon's society. As there exists no means of removing the l'Cie brand and the curse thereby imposed, Pulse l'Cie are hunted relentlessly.
When a fal'Cie takes a human to be one of its l'Cie servants, that person is given a Focus to be completed. Should the l'Cie fail to fulfill this Focus before his or her brand advances to its final stage, that l'Cie becomes a Cie'th.
Mired in eternal sorrow and regret, and robbed of all free will, Cie'th are damned to wander the world, unliving and undying, until their corrupted flesh at last can move no more. For Cie'th, there is no salvation.
The brands that mark a l'Cie as one of the fal'Cie's chosen change gradually, passing through several different stages. When the "eye" at the center opens - the brand's final stage - the l'Cie become a Cie'th.
A brand's rate of progression depends partly on the difficulty of the l'Cie's Focus. It is also linked closely to the individual's mental state, with severe psychological trauma sometimes spurring rapid advancement. In the most extreme cases, severe fear and shock at being made a l'Cie has turned newly made l'Cie into Cie'th at the instant of their branding.
For l'Cie, successful completion of a Focus holds the promise of eternal life in the peaceful slumber of crystal stasis - or so the legends say. Yet to spend an eternity as an immobile crystal is not so very different from death. The people of Cocoon consequently fear being marked as a l'Cie, equating the fal'Cie's brand with a death sentence.
Faced with only the choice between eternal damnation as a Cie'th and eternal imprisonment in crystal, it comes as little surprise that many l'Cie decry their fate.
These mystical entities reveal themselves before only a select few l'Cie. It is said that they are saviors, come to rescue helpless l'Cie who find themselves bound to a Focus against their will. If this is true, they offer a salvation few indeed would seek willingly: without exception, Eidolons attack the l'Cie whose presence they grace.
There have been no l'Cie in Cocoon for centuries, and as a result, no way of determining the truth behind tales of these beings. To the citizens of Cocoon, they remain the stuff of bedtime stories.
Lightning, Snow, and the others saw a phantom vision of this beast upon their branding as l'Cie. In the dream, they witnessed the creature besieging Cocoon's capital of Eden, but whether this was a glimpse of past events or a vision of things to come was unclear. What is clear is that Ragnarok is inextricably linked to their Focus. The nature of that Focus, and what must be done to fulfill it, remains to be seen.
Several hundred years ago, the armies of Pulse attempted to invade Cocoon in a conflict known today as the War of Transgression. The Sanctum's fal'Cie were able to repel the lowerworld forces before they breached Cocoon's interior, but not before they managed to seriously damage areas lying near the world's outer rim.
Details surrounding the clash remain shrouded in mystery, but the government's swift and decisive response to this violent Pulsian transgression minimized casualties and greatly boosted public faith in both the Sanctum and their fal'Cie.
In the aftermath of the War of Transgression, regions near Cocoon's outer rim were left uninhabitable due to the severe trauma they had sustained. To undo this damage, the fal'Cie gathered materials from the surface of Pulse and rebuilt Cocoon's wounded landscape using them.
Bodhum was one city so affected, and like the others, it still bears lingering traces of post-war reconstruction in the form of leftover lowerworld artifacts. The Pulse Vestige that hid a dormant fal'Cie was one such artifact.
- Added after defeating Alexander
L'Cie who fail their Foci become Cie'th, cursed to wander the wilds in a form of living death. Only after many years and much suffering do they extinguish the last of their strength and cease to roam. When this happens, the Cie'th's remains slowly fossilize, turning into what is known as a Cie'th Stone.
However, this transformation does not mark an end to the Cie'th's regret and sorrow at having failed. Even after having turned to stone the Cie'th cry out, imploring other l'Cie to fulfill the Focus they could not.
- Added after reading Mission description regarding any of the Undying
The Undying are fearsome Cie'th who, cursing their former fal'Cie masters for forsaking them at the end of their forced servitude, refuse to surrender their connection to this world.
Whereas normal Cie'th eventually cease their wanderings and turn to stone, the Undying rage on, fueled by a jealous hatred of all living things. Retaining the defiant strength of will they knew in life, they act on instinct, doling out death and destruction to all that dare cross their path.