Ghost stories seem a natural fit with some superheroes. Not so with the Flash. An origin based in science, scientifically trained alter-egos, villains who use technology. Even the “magician” villain, Abra Kadabra, is more of a techno-mage, using highly advanced future technology to carry out transformations that seem like magic to our experience. The closest the Flash mythos gets to the supernatural is the metaphysical nature of the speed force, and even that is described in terms of energy and the nature of space-time.
So it makes sense that for 1998’s “Ghosts” annuals, the Flash story would feature not a traditional ghost, but one tied to the speed force: Johnny Quick, who had vanished into the speed force two years earlier during Dead Heat.