We all know CC's story begins with Schala's diary, and also ends with the diary, which make the games looks like under someone's narration.
But could it possible that the diary does not actually have something to do with the game's story? As Kato pointed out, in those parallel worlds there would be respective developing stories. Perhaps that is just a way of description, the diary is not actually written by Shala or Kid in game, and that'll explain the inexplicable wedding picture on the desk.
Before the ending, Kid says(or Schala speaks in Kid's accent) she'll find Serge. That probably means in the new unified time line, she has not met Serge. And later, Serge awakes at Opassa Beach with Leena, that's before the time he ran into Kid. Then the the diary scene appears.
If the diary is written by Schala or Kid, there are still some problems to be solved: if she has the memory, she will certainly know where Serge goes, if she doesn't have the memory, well, how could that diary be written?
I – So for a good ending movie, you tried to use the crossing point of a young girl and her other side to imagine “a story in another dimension.”
Kato – Yeah, like that. I thought that was the perfect material to use to give meaning to a parallel world. In each independent parallel world there would be respective developing stories. If we did it that way, people at home could use the experience of Serge in the game’s worlds to think about the reality of their own world. Maybe somewhere in our world there’s a Kid, and surely someday we will find and meet. For a long time I’ve wanted realizations developed from games to not just stop with the game, and now I feel I’ve done it right. There’s a message that comes after the ending movie finished, and I hope that all players will understand these words that have come from my heart. That’s what I’d love to have happen.