I loved how he was the one to bring Aoife back down to earth. Here's a quote:
"So you've known me--what?---for more than four hundred years...and yet, what do you really know about me?"
Aoife stared at the slender black-suited man and shook her head. "Not a lot," she admitted.
"And why is that?" he asked.
"Because you were never interested," Niten said gently.
"You are the most self-obsessed, selfish person I know."
The warrior blinked in surprise. "You say that like it's a bad thing."
-The Necromancer, pages 337-338
This conversation started because Aoife commented on how Niten knew so much about cars, and he told her that he collected classic cars, and didn't she know that? And that really made him notice that she didn't know much about him. After a while, Aoife sits quitely for a long time. Then, she asks Niten a question about his car collection, the first time she's shown interest in someone else. I found this whole thing really cute, especially how Niten handled it cooly and gently, instead of just yelling at her about how selfish she was.
Niten is a very interesting character, and I hope we learn more about him in the next books.