Just Killer features a variety of elements, mainly the idea that ghosts exist.
There is more than one plotline. One plotline features Nathan Kinsecite, who was intended by Shipjos to be the main protagonist of the entire series. A different one stars Brian Hadont, who was in truth created by accident. The third plotline features four protagoniststs, Tom Moore, Zack Smith, Emily Wilson, and Max Miller. Each of these protagonists discover that they are Seers, meaning they are able to see ghosts (for ghosts in the series are invisible to most humans). Later, due to ghost-related problems, they are involved in many dangers, which they survive, but just barely. Throughout the series, they each try to overcome disaster while trying to learn what it truly means to be a Seer.