The concept of the anthro Pokemon itself is crucial. It changes the dynamics of the Pokemon - human relationship. The anthro Pokemon might have their own cultures, languages, and social structures. In many fanfictions, Ash has to adapt to these differences. For instance, an anthro Pokemon might have a very different view on battles compared to normal Pokemon, and Ash has to understand and respect that while still following his own goals.
The setting also plays a big role. Sometimes the fanfiction takes place in a new region or a different version of the Pokemon world. This new setting can introduce new rules or challenges related to the anthro Pokemon. Like, there could be areas where only anthro Pokemon are allowed, and Ash has to find a way to enter. Another important element is the character development of both Ash and the anthro Pokemon. They might learn new skills or gain new perspectives through their interactions.