I didn’t want Nightblood to come across as a “one ring” knockoff. He doesn’t turn people’s hearts or corrupt them. However, in order to be able to do his job and fulfill his Command, he needs the ability to determine who is good and who is evil.

This, of course, isn’t an easy thing to determine. In fact, I don’t think it’s a black or white issue for most people. When Nightblood was created, the Breaths infused in him did their best to interpret their Command. What they decided was evil was someone who would try to take the sword and use it for evil purposes, selling it, manipulating and extorting others, that sort of thing. Someone who wouldn’t want the sword for those reasons was determined to be good. If they touch the weapon, they feel sick. If others touch the weapon, their desire to kill and destroy with it is enhanced greatly.