Time in my world is... a largely unstable thing. If an event is altered in any way, everything that happens from that point onward is changed, including the memories of people. [This is actually more confusing and complicated, but he knows he should translate it into terms other people can understand.] There would also be records of timelines converging, people and things from one time period appearing in another, events that should not be logically possible occur, and making time unstable in the general sense. We call such events paradoxes.

With the Oracle Drive I found in the Paddrean ruins, I discovered that one of my friends-- Serah's older sister, in fact-- whom I thought was part of the crystal pillar was in fact alive and well in a completely different world, because I watched her fighting in that world. I don't know the complete story, but it seemed she had been captured by a paradox and somehow ended up in that world.

All I remember is her leaving us to crystallize, but according to Serah, she had been on Gran Pulse with us when everyone began to evacuate Cocoon. I remember Serah being happy one minute, announcing her plans for marriage with her fiance, and the next minute crying because her sister was gone and I...

I was the one who told her that her sister was part of the crystal pillar, and she didn't believe me.

[He should have known back then that there had been something wrong with the situation. But he didn't.]