Aang being the titular character of the show has a lot to do from the very start. First, his entire nation of Air monks has been completely wiped out by the Fire nation, so does he rebuild? He has been in a hibernating state for the last 100 years, allowing the Fire Nation to take control and commit atrocities when left unchecked. How does he deal with his guilt over running away from his destiny? Finally, how does he restore balance to both the physical world and spiritual world while also finding masters to help him learn to bend the other elements? I love how despite his changes in the show, he maintains a peaceful and harmonious outlook no matter how awful things become.
