For purely fictional names, the requirement is that the name must be notable enough. A general rule of thumb is that the fictional character should be notable enough to have a page on
Wikipedia.org (or a dedicated subsection on a page). Wikipedia has a lot of editors who vigorously debate notability, so they can "do the work" in a way for the small pool of editors here.
Of course, if you can find any real bearers then you can submit the name on that basis.