Even though the game's publisher Naughty Dog hasn't officially announced anything yet, well-informed sources explain that the motion capture is about to begin, so the casting for the very secondary characters (for the moment).
Casting motion capture in progress for The Last of Us 3
The casting announcement explains that the scene to be shot features a group of scavengers who live on the outskirts of a town in a Victorian house used as a base. There would be five characters involved, conflicting over how to organize the group, including "a young woman, an ex-soldier, and an affable man who turns dark."
If the announcement does not mention Abby (a central character in The Last of Us II), another source specifies that Ellie, heroine of the series, is at least as essential in this third part as it was in the previous game.
Again, Naughty Dog hasn't confirmed anything except that the studio is currently working "on an all-new single-player gaming experience," which many experts believe is The Last of Us Part 3. follow, therefore. Source: Forbes
