Vaan is more of the narrator perspective rather than an actual main character. This isn't really his story at all. Its more the story of Ashe and the resistance as a whole, which Vaan plays a strong role in, if only on accident. Otherwise, he is simply another face in the story, nad as the story progresses, he begins to play less of a role more and more rapidly. I haven't finished the story yet though, so he may make a bit of a comeback.