special ending *spoilers*

quote Alkor

quote Caius

What will happen in your future already happened in my past

That's what he said after saying Lightning is dead.
In this ending, he's on Etro's throne, this is the place where Lightning should be at the end of the game, but she's not. The timeline is random in Valhalla, so we can only guess when this ending really happens. For us, it's after the chaos reached pulse, but for him, we can't say.

There are strange things in this ending anyway :

• He's talking to Yeul, but she's not there.
• His eye has the red color of his heart, this power isn't mentioned anywhere.

I saw it 1 or 2 hours ago, so for now it's still fresh. I guess I'll record it to find other strange thing in it later.

quote The Pursuit

THe reason she is sitting on the throne is because it symbolizes that the worlds very existence relies on her to embody the divine will. As Lightning wants to maintain hope, she enters the crystal stasis in order to protect the will of her sacrificed sister.

That is what the behind the scenes section of the book says. It also says that they will be releasing a DLC to reveal the background of it.

quote Fire Fox

I just forgot to say, Serah's death was pretty dumb in my opinion.