" 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. " - Datalog: Pulse l'Cie
L'Cie are servants of the fal'Cie and when chosen by a fal'Cie are subsequently branded. The brand differs depending whether the fal'Cie is a Pulse or Cocoon fal'Cie with the former type of l'Cie being feared as harbingers of death and destruction, tasked with destroying Cocoon for their immortal masters.
Upon the moment of their branding a l'Cie is given a Focus by the fal'Cie who chose them; essentially a task they must perform. If they do not perform this task within a certain time limit, notified by the brand changing over time - once the eye in the center is fully opened, the end is near - they will turn into mindless, shambling Cie'th, beasts who wander eternally, trapped in a hulking body that was grotesquely deformed as a punishment for failing their Focus. A person's mental state has an impact in the acceleration of the time they have, so much so, that the shock from being chosen can cause a person to instantly transform into a Cie'th at the moment of their branding. Should they successfully fulfill this task however, a l'Cie is blessed with eternal life by being turned to crystal to dream away their days. Sadly, many believe this is little better than being turned Cie'th.
In order to complete their Focus, l'Cie are given tremendous magical powers which come from the power of crystal. Their strength surpasses those of ordinary humans so much that l'Cie are either feared or revered depending what kind of l'Cie they become. They can also be given Eidolons - beings with incredible power who exist to serve their l'Cie - but they must overcome a test of mental fortitude and strength of will before they can command them.