In Chapter V, after you have found all seven chosen ones (Ragnar, Alena, Brey, Cristo, Taloon, Nara, and Mara), you can change the music on the overworld. Place Ragnar at the lead of the party if you want Chapter I music, place Alena, Brey, or Cristo for Chapter II music, Taloon for Chapter III, Nara or Mara for Chapter IV, and the Hero for all-new music. If you want the Hero's old music, set him/her at the head of the party with no one else in it.