Thanks to arciele for the inspiration!
Maybe you’re wondering what each of the games in the Final Fantasy XIII trilogy have to do with each other. Lightning is in each game, but the trilogy doesn’t seem to be about her or her friends. And the story only seems to have limited continuity. So why the sharp tonal shift in the three games?
Arciele thinks:
the head-Canon I use to make sense of the FFXIII series (or Lightnings saga) and how it shifts so dramatically between games is that when they decided it would become a series, they chose to dedicate each entry to different fal’cie.
So XIII (already released) focused on the interplay between Pulse and Lindzei as their minions sought to reawaken them/find Etros gate
XIII-2 was focused on Etro.
And LR:XIII was entirely Bhunivelze.
And it’s for this reason that the main antagonists of each game are based on those same deities. Barthandelus/Orphan stem directly from Lindzei (and were created by him?), whereas the characters overcome their focus, which stems from Pulse. Caius possesses Etro’s heart. and God is God.
On the other hand, the protagonists are also related to the focus deity. Pulse l’Cie in XIII, “servants” of Etro in XIII-2 especially Serah with her Eyes (and Lightning as her champion), and Lightning as the Savior, servant of Bhuni
Not sure if that really makes the story any better, but I feel like it makes more sense
Pulse, Lindzei, and Etro are the original fal’Cie created by the god Bhunivelze. According to the mythology:
The original “fal’Cie” created were Pulse, Lindzei, and Etro: Pulse and Lindzei were given powers to create and, according to the mythology, created many fal’Cie of their own, while Etro was discarded and killed herself. Pulse and Lindzei retreated to an unknown realm, leaving their respective fal’Cie to carry out their tasks.
This makes sense for Final Fantasy XIII, as
Pulse is said to have created the world where Final Fantasy XIII and Final Fantasy XIII-2 take place, and it used to be worshiped by many of the tribes inhabiting the world, who named the planet after it, calling it Gran Pulse.
But here, I break with arciele. I think the main focus is on Lindzei. According to the seeress Paddra Nsu-Yeul:
Analects – Her Providence
Her Providence sought nothing.
Her Providence made nothing.
She but looked on, silent in Her sorrow.
The Goddess pitied mortals, destined as they were to die, and so She deigned to intervene in the hour of their greatest peril. She averted cataclysm that was to be and put to rest the ones who would have robbed so many of what time fate had ordained.
Her compassion did not end at this.
The Goddess pitied also those subjected to that fate of Focus, crueler still than death. To them She sent Her messengers, to deliver hope when all was lost.
The two messengers were Fang and Vanille.

Final Fantasy XIII-2 is more about Man’s creativity. Lindzei invokes and encourage creativity and innovation through the minds of humans, shown through the technologically advanced civilizations ruled over by the deity, which describes the advancements of Cocoon throughout the years.
Etro’s influence is prominent in each game, most specifically Final Fantasy XIII-2. But she’s most evident in the last part of the trilogy because of of Bhunivelze role in the game. Bhunivelze was actually looking for Etro’s Gate to become immortal. His plan was to
“condition Lightning into an emotionless replacement for Etro to oversee the balance of life in the new world”
But he failed.
Bhunivelze isn’t a fal’Cie. Yet the entire trilogy is about determining one’s own fate. It makes sense for Lightning Returns: Final Fantasy XIII to end at a god’s defeat. With gods, death is a bit different. Etro could take her life, and fail as a protector. Pulse died with the fal’Cie killed in the game. Lindzei died when time stopped, and humans could no longer innovate.
All gods eventually die when we forget them.
When Lightning creates the new world, she erased the concept of fal’Cie and the deity Bhunivelze for good. This is one of the reasons we must not forget Lightning, as the creator of our world. As this, perhaps Lightning was actually the creator of Eos, and maybe she’s the god of Noctis.