Shawn is very optimistic and cheery, but not the smartest. He always manages to brighten up people's days and trusts people really easily. Even though he seems like the perfect happy person, he has a dark past that gave him PTSD. The incident connected to it was that his house was on fire, and his parents were burning alive while he just sat there, not being able to move because he was paralyzed. 

Later in the story, his PTSD lets him go crazy and slowly goes insane, as he changes into one of the main badguys when Zeraphine and Airen try to save the world [AKA last stage of story.]

He becomes evil together with his dead father, whom is now a spirit, who manipulates his son into helping him, since he, as a human being, still has an useful purpose.