We know Moon Shadow to be our protagonist because he is the one we most relate to, the one we feel closest with and root for throughout the story. It sure helps that he's also our narrator, and a trustworthy and self-reflective narrator at that. Like most protagonists, we follow Moon Shadow as he faces new challenges and works to get through them. Similarly, we follow Moon Shadow as he meets new people and figures out what his relationship to them is. Basically Moon Shadow is our tour guide through Dragonwings and we're super-glad he is. Who knows what might happen if Black Dog, for example, were our narrator?