Here's a brief summary that I wrote up based on what I can remember of the Mystery of Mew. How does this sound to you?

[quote]Aaron is largely a friendly, selfless Pokemon. He tries to maintain all of the qualities one would expect of a knight. He does his best to be strong, honorable and strives to be a true paragon of the Pokemon world. However, this can lead to him taking on more than he can handle. Compounding on this problem is the fact that he will often attempt to take these problems on by himself, whether it's because he doesn't trust them to handle it, because he doesn't want to put others at risk, or simply because it's something he wants to accomplish his goal in his own way. This can lead to him leaving Pokemon out of the loop when he takes action, for better or for worse. However, this could put him at odds with other Pokemon that he works with.[/quote]

It's pretty brief, but as far as I can remember, Aaron doesn't really have much attention put on him during that movie; it's all about Lucario and Lucario dealing with being left behind by his mentor.