Well I understand that not many people had high praise for this game. I thought it was enjoyable but the ending seemed... well it placed me on the fence. I've heard a few others claim that its trying a bit too hard to go for the kingdom hearts "nothing makes that much sense but its cool anyway" vibe. Though I never got that vibe since I never bothered to play a Kingdom Hearts game.
And the reason that Aya acts differently in this game is kinda obvious once you beaten it...