Below is a copy and paste of an IGN comment by a user (not me) named xwadwadw. I posted this because it's a decent summary of the info you can gain from the datalogs of the FF13 series, which explains the overall plot of the trilogy much better than actually playing the game does. It is fairly interesting and at the same time such a disappointment when you realize how many different ways they could have approached that plot to tell a much better story with a better main cast than the games had. It's a shame because obviously a lot of effort went into writing the mythology of the game and so little went into the actual script in the 13 series.
"Here let me help you. This should make everything about 13 easier to understand.
Much like that of Roman Mythology, the universe of Final Fantasy XIII is divided in two - the Mortal World and the Unseen World (the realm of the dead). In the beginning there was the Goddess Mwynn and her son the god Bhunivelze. Bhunivelze, lusting for full control over the Mortal World, killed his mother and in her death Mwynn was sent into the Unseen World.
This hostile takeover was successful for Bhunivelze, but it didn’t come without a cost. He had become extremely troubled at the thought that Mwynn might have placed a curse on the realm of the living so that it would one day be destroyed. To ensure this would never come to fruition, Bhunivelze sought to destroy his mother once and for all, but was unable to reach the Unseen World without losing power over the Mortal World. To find the entrance to the realm of the dead, Bhunivelze created the fal’Cie Pulse and tasked him with searching the Mortal World for the door to the Unseen World (now known as Etro’s Gates).
“Gran Pulse” is a planet that was named after the fal’Cie Pulse.
Pulse, also known as “Hallowed Pulse” and affectionately referred to by many as “the Maker,” is one of the high deities of Final Fantasy XIII’s mythology. According to the in-game Analects, after being created by Bhunivelze, Pulse created the world where Final Fantasy XIII and Final Fantasy XIII-2 take place.
Pulse is indeed a fal’Cie (the first of his kind), but is known as “The Maker” because he also birthed both the world of Gran Pulse and all of the fal’Cie that inhabited it. His created fal’Cie all hold specific functions, but ultimately they all follow the same mandate of attempting to locate the door to the Unseen World.
While he has seemingly abandoned the world of Gran Pulse, it is made clear that he returned briefly to bind Lightning’s fal’Cie (they were all selected by the fal’Cie Anima, but bound to their Focus by Pulse himself).
No. To assist Pulse, Bhinivelze created the fal’Cie Etro. Soon after her creation, Bhunivelze realised that he had created here in the same likeness of his mother Mwynn. Bhunivelze stripped Etro of her powers and created the fal’Cie Lindzei soon after. Lindzei would be tasked with protecting the Mortal World and Bhunivelze himself.
With his fal’Cie at work, Bhunivelze put himself into a deep crystal sleep, only to be awoken once the door to the Unseen World was found.
Pulse and Lindzei were busy creating and exploring the many landscapes of the Mortal World, but Etro was lonely and depressed as she lacked purpose. In despair, she killed herself and disappeared from the Mortal World, entering Valhalla (the Unseen World). From Etro’s spilled blood, humanity was born and soon flourished. She felt a close bond with these creatures as they, like her, were destined to perish.
In the Unseen World, Etro eventually found the Goddess Mwynn. Mwynn was being overtaken by a strange energy mass known as “chaos.” Before drawing her last breath, Mwynn tasked Etro with protecting the balance of the universe, for if the balance between the Mortal World and Unseen World were disrupted, the universe itself would collapse. Unbeknownst to Bhunivelze, the demise of the Mortal World was not a curse by Mwynn. It was predestined to occur.
Now considered to be the Goddess of the Unseen World, Etro would greet those who died and passed from the Mortal World to Vahalla with a piece of chaos to hold inside them. This piece of chaos inside of every human came to be known as the “heart.” Providing that humans continued to be born and die, the universe would remain in balance.
Pulse continued to craft the world as he saw fit, while Lindzei created the floating paradise of Cocoon for the safekeeping of Etro’s humans. According to the Analects, Lindzei created Cocoon from piece of land taken from Gran Pulse’s soil. From then on Lindzei bore other fal’Cie within Cocoon to take care of those humans. This act was seen by the surviving denizens of Gran Pulse as a grand betrayal. Notes left behind see them viewing Lindzei as a villain and Cocoon as the “Viper’s Nest.”
One day, Pulse and Lindzei left the Mortal Wolrd, never to be seen again. The Cocoon fal’Cie (of Lindzei’s brood) wrongly assumed that the two had absconded to the Unseen World where Etro resided, however Pulse at least seems to exist on a Historia Crux-like plane of existence beyond Valhalla and the Mortal World.
Where it appears that the only way to enter Valhalla (the unseen world) is to die, the High God Bhunivelze will likely sleep until the end of time.
Etro loves all of humanity as they are the only beings who understood her plight, but yes - had Fang had succeeded in destroying Cocoon and ending humanity, the universe itself would have come to a premature end.
Etro saw the Unseen World as being filled with chaos and sought to correct the balance by infusing humans with lesser pieces of chaos. This way, she could ensure that the substance was dispersed between both the Mortal and Unseen World. If all of humanity were to simultaneously die, Etro’s Gates would not open (as the Cocoon fal’Cie wrongly assume). Instead, the Unseen World would be overrun with chaos, the balance would be lost, and the entire universe would collapse as both worlds faded into nothingness.
When given their focus, the party believes they are meant to turn into Ragnarok and destroy Cocoon. However, this doesn’t make sense in the scope of the game. Pluse, the Maker, was responsible for creating the world and seeking Etro’s Gate for the God Bhunivelze. The destruction of Cocoon at the hands of Ragnarok would result in the universe collapsing and Bhunivelze’s death. Why would Pulse ever want such a thing to occur?
The answer is actually pretty simple: his goal was compromise. Pulse, in his divine omniscience, knew that as long as Cocoon’s fal’Cie existed, they would seek the destruction of Cocoon and all of it’s inhabitants. The only way to stop them from continually initiating further conflicts that threatened the balance of the universe would be to destroy them. Unfortunately, in doing so, Cocoon would also die. In recognizing this, Pulse enlisted Lightning’s group with the goal of ending Cocoon while saving it’s inhabitants.
The true focus was completed when Vanille and Fang became Ragnarok and encased Cocoon in crystal - forming a supporting pillar to ensure it wouldn’t fall from the sky unto Gran Pulse. Lightning’s party was crystallized by Cocoon’s end, only to be awaken with Dajh and Serah from their crystal stasis shortly thereafter.
This release from crystal stasis was Etro’s final gift.
The act of mercy Etro bestowed on Lightning and her group at the end of Final Fantasy XIII cause a distortion in time, allowing the chaos of the Unseen World to grab Lightning from the Mortal World. Etro was able to minimize the damage and subdue the chaos, but Lightning was trapped in Valhalla and eventually charged by becoming her protector as she was forced into a deep rest.
Etro was praised by Gran Pulse’s oldest tribe as their patron goddess. This tribe would birth one girl every generation with a gift known as the “Eye of Etro.” This power allowed her to act as a seeress, capable of seeing the future at the cost of her own life. Each generation of Yeul would be aware of future events, but unable to change them. A l’Cie Guardian was assigned to protect her while she lead the tribe.
The last Guardian, Caius Ballad, was freed from his l’Cie fate by Etro who placed her own heart within him, granting him eternity to protect Yeul’s reincarnations until the end of time. It is revealed that a seeress’ life span shortens the more the number of possible futures grown and that’s why Caius will eventually try to reduce the number of possible futures to the point where there is only the on inevitable future left: world destruction.
Caius declares ware on Etro and master-plans the means to destroy her and shatter reality. He begins by entering Valhalla and battling Lightning.
Note: The official Square Enix statement is, “fal’Cie are an existence beyond human comprehension, possessed of incredible magic power.” I’m not sure that description does them much justice, though. Like in most other polythesitic religions, the fal’Cie basically exist as “lesser gods” (although, you could think of them as angels if you’re of the Christian or Jewish persuasion).
Concludes with Lighting Returns."
