Jason was born second, after Ellieona. He was born one day less than a year after her. When Ellieona disappeared for the first time, he was six and she was seven, leaving him as the new heir. Ellieona blames herself for how he turned out, thinking she destroyed him by leaving. Jason is first seen in Amanda's chapter, asking her to marry him instead of his younger brother, in order to unite the two kingdoms. She cruelly turns him down, leaving him angry and insulted.
We don't know how or why Jason turned out evil. But in the end, he becomes their biggest threat to stopping Apep. Becoming half devil, he appears to the five in their moment of greatness, attempting to shatter Ellieona. She starts crying and blaming herself, only snapping out of it when the others convince her it was not her fault.
Jason is said to have been destructive, always finding ways to break Ellieona and his younger brother Joshua down. Jason for some reason, wanted Ellieona with him in his castle. Whether to mock or to recreate a family like setting, this is unknown. Jason ends up murdering Laine's sister, April, to trick Laine into bringing Ellieona to him.
In the dream worlds, Jason was not seen as evil and destructive. He got along with Carson and Joshua, supported Ellieona, and played the role of the elder brother.