Avatar: The Last Airbender - Smoke and Shadow

Avatar Aang asks his friends to help him honor Yangchen's Festival - an extremely sacred Air Nomad holiday that has not been held in over a hundred years. However, cryptic visits from the spirit of Avatar Yangchen herself lead Aang to discover a jointly owned Fire Nation and Earth Kingdom refinery - operating on land sacred to the Airbenders! Is this the cause of the pollution Aang finds there or is something more mysterious happening?

From Dark Horse: When Aang leaves to aid Fire Lord Zuko with spiritual affairs in the Fire Nation, Katara and Sokka return to the Southern Water Tribe by themselves, where they are shocked to discover that their village has become a bustling city, with Hakoda in charge. The changes seem to have largely been due to the efforts of Malina, a member of the Northern Water Tribe who is seemingly striving for greater unification of the Water Tribes, but has unknown intentions.