A piece performed on traditional Korean instrument called a gayageum, which is developmentally related to instruments larger than a western dulcimer.
AS the poster noted in a comment, these are like the Japanese koto, the Gucheng (China), and Dan Trank (Vietnam). From Korea there is also a very interesting one called Komungo, and one similar in shape but played with a bow called Ajaeng.
In a comment by the original poster, performingasia, they noted:
well, I posted the video but I am not the person playing it. I took a 3 months Gayageum workshop at the National Center for Korean Traditional Performing Arts in Seoul. The person in the video, Eun Sena, is a teacher at that Center. She kindly allowed me to take this and the other videos.
This is a traditional fan dance, where you get some idea how the traditional dress, the hanbok, functions in dances, and how larger instrumental groups sound. The camera work is amateur, but watchable. Whoever arranged the choreography did a beautiful job.