Not sure if it has been mentioned much in the thread, but I highly recommend everyone with an interest in lore to do the Shadowed Past side quest that unlocks after you do 6.2, just below the Meghaduta.
Was really cool seeing the histories of Scarmiglione and Barbariccia, along with how Golbez got them to his side. Looks like it will be continuing it too, so likely see more of the other Fiends backstory after we dispose of them.