Twice - TT by Haegeum (Queen TV : Yoolee)
Haegeum is one of the Korean traditional chordophones. The way it works is similar to cello but it has higher tone.
Queen TV is Fusion Korea traditional music group and also promising Youtube channel uploading Korean traditional instrument playing video they performed.
Want to see more gayageum play ☞ https://goo.gl/LLE2JK