THE mermaid show started with Miria's beautiful aria. But it didn't stop at the introduction. It continued on until Lauren and Astrid appeared in the pool. The story began there.
As Miria sang, Lauren and Astrid interpreted it by moving around the pool. Although Miria was singing without lyrics and doing it purely by A Capella, the message she wanted to convey still reached the audience. It's not only because of the emotions filling the air as she sang, there was also the fact that Lauren and Astrid were perfectly interpreting every emotion as they moved in the pool.
As the audience understood it, the story the three were portraying was that of two mermen being star-crossed lovers and Miria was the narrator telling everything with her song. Of course, anyone could have a different interpretation. But the majority had the same idea.