[quote=@Saarebas]
[@Mattie_] Hmmm what would our local soul dealer get out of this relationship?
[/quote]

Narza fuses with souls to grow stronger, but normal human souls will start providing less and less of a boost. She'll wanna go for better stuff, big meals like giant souls, or delicacies like High Elf souls. 
So if she set up a deal with Azavarn, she could steal and keep normal human souls and exchange them for rarer ones. Or forcibly take the souls of people Azavarn has failed to trick souls away from. 

What do you want to happen to soulless entities? Be comatose vegetables? Because those that Azavarn contracts with still function fine...