I also took Perform: Sing for my Nierite. Using an ancient 'maritime' culture like the Phoenicians, the lyre, harp, or double-flute are options.

I've thought about a fife. Any instrument that can set up a quick tempo that people can get into will do. Or dance to for that matter. Thanks to everybody for all the comments thus far. And if we want to get into a general discussion of the Undir and their culture I'd be cool with that. Let me know and I'll start a thread/post.