Avril, Eli, James, Tiffany, and even Eve have all been living in my mind palace since 06, albeit under different names.
They were all originally created as main characters for an old story known as HMD. A story which eventually went through massive overhauls, and became Soul to Call. Naturally a handful of HMD characters were carried over, though their personalities, back stories, and relationships also went through enormous changes.
Marcus is the only really “new” character created for Soul to Call.