I really hope its Window. I felt like Suikoden ended without giving too much closure to Window's story. He went off to design stained glass windows... for who? Where? Did he have to travel far? Was he famous for his role in the war? I wonder if his perspectives changed. Did he "see through any new windows"?
I feel like Window could find the True Window Rune, it would be so awesome. His attacks would use glass, and you could create art. There could be minigames where you color in a stained glass window like Mario Paint ore something. Just think of all the possibilities.