Except it has been proven that some demons are in fact capable of love. Sandre and Caera actually do care about each other. Not sure if it applies to Kas though since she isn't from our world.
I use the titanic hat, bodysuit, two lucky strikes, sheildsplitter, cloak of winter, and I have blue flame blade, cleave, steady strike, deadly shadow, and assasinate. My thief demolishes almost every encounter in 1-2 hits.
I managed to hit the real whisper by pure luck and one ability in particular allowed me to beat him. Equanimity one of the abilities you get from Zo which boosts both crit chance and crit damage. I had a black mage set up so I used that as well as grease and fireball so when it crit it...