Brandon Sanderson
Chapter Thirty-Five
Vivenna Awakes, Bound by Vasher
This chapter—with what happens in the latter part of it—is the most dangerous in the book. Dangerous to me as an author, I mean. I love good plot twists, but I worry about leaving them without proper foreshadowing. I've never done something as drastic as I have in this book, having a group of sympathetic characters turn out to be working for the wrong side. I hope it succeeds, but I know that if it doesn't, readers will be very mad. Nothing is sloppier than a book with unearned changes in character motivation.
But we're not there quite yet. Before that we have the first real interaction between Vivenna and Vasher. He gives her what he likes to think of as the Nightblood test. One nice thing about having a sword that "cannot tempt the hearts of those who are pure" is that when someone like Vivenna touches it, she gets sick. 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.
Nightblood himself, unfortunately, doesn't quite understand what good and evil are. (This is mentioned later in the text.) However, he knows that his master can determine who is good and who is evil—using the sword's power to make people sick, or through other means. So, he pretty much just lets whoever is holding him decide what is evil. And if the one holding the sword determines—deep within their heart—that they are evil themselves, then they will end up killing themselves with the sword.
Vivenna passes the test, which surprises Vasher. He thought that she'd be the type who would use Nightblood to kill and destroy. (He doesn't have a high opinion of her, obviously. Of course, that's partially because he's let his temper dictate what he thinks.)