THAT'S RIIIIIGGGGGHHHHHHT!!! ~ LIGHTNINGS BACK IN HER FINAL CHAPTER!! (Of at least her bit in the "Fabula Nova Crystalis"/XIII FF series!!!) (Remember, we still need Versus
XIII and Type-0 of the series!)
So, I saw the trailer! Very short! But to the point. Let us begin-
The trailer starts off with an unknown Europeon style city, and then train station. Very modern day! At the train station Lightning gets off the train, look very much like an Assassins Creed Ezio cosplayer!(Ok, so the coat she had in the first game is a trench and her cape is longer) Lightning narrarates "Thirteen days before the world ends, I have awakened."
The narrarotor then switches to a young mans voice and explains the city. I don't remember the city's name but here is what goes on. It is a beautiful city, rich and vibrant. It's citizens are all faithful to God, but underneath the suraces lies darkness. For those who don't believe in God.
The trailer then goes off to Lightning exploring the city, fighting, and a clock is shown going backwards.
At the end, Lightning is talking to an unknown person saying. "I'm sure you know who I am, or at least - what I am."
That's where it ends.

Hints/Thoughts:
The game looks stunning, obviously. Yet, I am SO surprised by just how modern the city look like! It looks like a little town in Italy or another part Europe! Street lights and all! The ppl look just like you or I! Yet, there are a few that do wear intricate clothing and carry weapons. So in a sense, Lightning doesn't stick out like a sore thumb.

The clock face and the 13 days before the world ends.
The clock is shown going backwards, so maybe it will be similar to Majora's Mask? Maybe Lightning has to reverse time before the 13 days are up to change the worlds fate? It's understandable, since she is in a clock tower in the end of the trailer.

How Lightning will battle this time around.
Despite the city being modern, there are monsters. However, to be honest...I have no clue as to how a city like it would have monsters. Especially the big ones in the trailer. Anywho- Lightning DOESN'T fight with a gunblade this time! Oh no! She is a classic this time around! SWORD AND SHIELD BABY!!! (I wonder what Warrior of Light would think of that? How "fairytale" Lightning~ *gets hit by a Lightning punch*
The battle system looks like the other games, so no new battle moves YET.

ALL IN ALL:
I'm very interested on how this will be all about. Why 13 days before the world ends? Why will the world end? And above all (for me at least) - HOW DOES THIS TIE IN THE FABULA NOVA CRYSALLIS AS A WHOLE?
I mean, in XIII-2 Lightning serves Etro, the goddess of Death in FF Versus XIII universe. So, in FF Versus XIII, will their be a tale of "Etro's warrior"?
Also, how will it tie into Type-0? Perhaps, the city where Lightning is, will one day be the city in TYpe-0?
Hmm, well all theroies. But I look foreword to it a lot!