The focal character is, more than anyone else, "the person on whom the spotlight focuses; the center of attention; the man whose reactions dominate the screen.
"[1] For example, in Gaston Leroux's The Phantom of the Opera, the protagonist is Christine Daaé (the audience is concerned mostly with her emotions, aims, and well-being), while the focal character is the "Phantom" (the audience is concerned mostly with the allure of his actions and reactions—though to some degree, later on, his emotions as well).
The focal character of the story is Roderick Usher, whom the reader cares for more greatly and follows his condition and emotions more.
In Sir Arthur Conan Doyle's works of Sherlock Holmes, Watson is the viewpoint character, but the story revolves around Holmes, making him the focal character.
Betty is the character who is always involved in the main plots and mysteries of each season, and even as the series progresses, her family becomes the central focus of the show.