The guzheng or the zither?
The instrument Lan Zhan plays is actually called a Guqin. It is a zither type instrument but very different in tone and sound to some European zithers even the guzhen. Guqin is probably my favorite Chinese instrument
Here are some of my favorite covers played on the guqin.
https://youtu.be/TnXmB3G6g_s
https://youtu.be/ntIYLLlVGMc This one I can just imagine lan zhan playing ♡´･ᴗ･`♡
https://youtu.be/EkP-I2D0Pcw
https://youtu.be/_9fnek_hjR8
His instrument is a qugin called 'Wangji'
Yep, that's right! Lan Wangji plays a guqin. If you're courious about it and haven't watched it yet, I recommand you give The Untamed a go and see it in action! You can see it in the animation too, but I personally find the effect to be a little bit different. In short, the guqin kinda sounds like... a chinese version of the harp, very celestial and oriental.
So I found out on the Exiled Rebels Scans website that Lan Zhan’s instrument was called a zither (but it looked more like a guzheng from the angles shown but the length is different) and does anyone know any professional musicians that can play this? (It’s a rare instrument now and it’s apparently difficult to play) I wanna know so I can look it up and listen to it on my phone! (っ°Д °;)っ
Edit: okay, okay, I’m sorry that I’m not up to date on the appearance of Chinese string instruments! The translated story on the website I read said that he played a zither but in the manga and the anime he plays what people are telling me is called a qugin.