In the drama, the scene where Xia Yu and Yan Ni dance ballet together is a combination of special effects processing and actual shooting. First of all, Xia Yu and Yan Ni only filmed their facial expressions and movements on stage, while the jumping movements were done by professional ballet dancers. Secondly, the post-production staff synthesized Xia Yu and Yan Ni's facial expressions and movements with the dancers' jumping movements through special effects processing, making the whole scene look smooth and natural.
So, although Xia Yu doesn't know how to dance ballet, the ballet dancing scene presented in the drama was realized through a combination of special effects processing and actual shooting.