Quick quotes: Kitase on Lighting & Serah's "sisterly love" in FFXIII-2
"As far as how the sisterly love is depicted, I think that you will have a better sense of it once you play the game. As far as the differences between how they express their affections for each other, in Final Fantasy XIII Serah was a Crystal and Lightning, as an older sister, was trying to save her. Whereas Serah goes out looking for Lightning this time, who has mysteriously disappeared, it seems everyone has accepted the fact that she is gone, but she is determined to find Lightning and she has set off to go look for her. So you can tell that they are sisters, that they have similarities, strong determination and a strong core." - Final Fantasy XIII-2 producer Yoshinori Kitase, speaking to RPGSite (via FFN) at a recent media event.