A weapon that gets defensive and spellcasting abilities when upgraded (like Dak'kon's sword when you're treating him well)?
Exactly, and it would be darned unfair to make pacifists and diplomats to kill to upgrade their weapons. Isnt there a way to not kill mooks anyway (capture them and put them in your prison)? So, whatever you do to not kill in those cases can be made game wide where you simply beat them unconscious with the flat of your blade, or like. Otherwise, like kill xp, this will literally force people to kill every living thing on the face of Eora.