There are many episodes in Tian Xia Wushuang, I don’t know which one you are asking about. A solitary shadow in the world is a very classic suona song. Well, it’s the overture. The song "Just Suddenly Lonely" is available on Kuwo Music, just search for the Tian Xia Wu Shuang original soundtrack. There are also many cover versions by singers that are also very good.