Denth the Traitor
Denth was always going to betray Vivenna. In fact, this is one of the very early concepts for the book—the idea that I wanted a bad guy who was not only likable, but funny. Too often, villains are portrayed as simply despicable people. If they laugh, it's evil laughter.
But people just aren't like that, not most of them. They're real, they have goals and motivations, but they also laugh, cry, and feel. Denth is a mercenary. More than that, he's a man who has caused a lot of pain and death in his long lifetime, and he copes with it by letting himself be hired to do important tasks. So that he doesn't have to feel as responsible.
In a lot of ways, I imagined Denth as the anti-Kelsier. Glib, smart, and hired to do impossible tasks. Only in this book he works for the wrong team. In this scene in particular, he was doing his best to nudge Vivenna to give him the Breaths. His job was only to hold her, to keep her captive and in reserve just in case the plots with Siri failed. That way, there would be a second princess to use in the plots. He was assigned to work for Lemex originally just to give him an in with the Idrians in the city, so that he could rile them up to incite the war further. But when he found that Vivenna was coming, he realized that she would be a much better pawn, and so he poisoned Lemex and took her instead. His employers were very happy to have a backup princess.
So, anyway, Lemex's Breaths were secondary. Denth wanted them, but he knew that the most important thing to do here was get Vivenna to trust him. So he tried to subtly manipulate her into giving them to him. (He intentionally acted reluctant to take them in order to goad her.)
In some ways, even though he doesn't have a viewpoint, a big theme of this book is the tragedy of the man Denth. He could have been more. At one time, he was a much better man than most who have lived.
Tonk Fah is a waste of flesh, though. Even if he is funny sometimes.