The walkers in The Walking Dead comics did evolve. Their behavior, appearance, and abilities changed as the story progressed, adding more complexity to the narrative.
In The Walking Dead comics, walkers are silent. Their presence is more about their menacing actions and the threat they pose rather than any form of communication through speech.
Survival is a very common theme. Since it's set in the post - apocalyptic world of 'The Walking Dead', OCs are often trying to find ways to stay alive, whether it's from walkers or other dangerous humans.
Since it's an OC fanfiction, the main character is likely the Original Character who is immune. But there could also be other characters from the Walking Dead universe that interact with the OC. Maybe Daryl, who is known for his survival skills, could be involved. He might be initially skeptical of the OC's immunity but later come to rely on it.
An OC could fit in by having useful skills. Like being good at hunting or knowing how to make weapons. That would make them valuable to the group in the fanfiction.