It could mean a fan - created story where a character or characters come to consider a particular place as their home. For example, in a superhero fanfiction, a hero who has been on the move might finally find a city or a hideout that they start to call home, with all the emotions and relationships that come with that concept.
Well, fanfiction often takes existing fictional universes and expands on them. 'To call a place home' in this context could be about how a character in a well - known story, like a character from a popular TV show, starts to see a new or different place within that fictional world as their home. It could involve them adapting to the culture, the people, and the physical environment of that place.