The plane of fiction is part of the collective Imagination. They tend to be separate existences, created by the writers and readers/viewers of the work and their devoted interest to the stories (you know those stories that you just lose yourself in). Imagination is used quite frequently in magickal workings (visualization, for one, can be simplified as glorified make-believe) though the word carries a bit of stigma to it, implying that what you experience is not real. To tap into a specific fictional work will bring you to a limited plane. Books and movies end, and my theory is that they constantly loop around and around, with variations in pattern depending on personal interpretation of the story (for example, sympathizing with Voldemort versus Harry).
If you get into Chaos Magick you may find working with the archetypal energy of fictional beings much easier than from a more conservative standpoint. Because most fictional characters are meant to represent and exhibit certain qualities, and because of their artificial intelligence (meaning they are designed, versus autonomous) they are neat little packages of symbolism and energy to draw from.
Check out this person's experience invoking Buffy the Vampire Slayer for some inspiration: