The mermaid represents a "living resource." The king views her life as a commodity to be consumed for his own preservation, mirroring his exploitative view of his people and his own illegitimate daughter.
At its core, the film explores desperate quest for eternal life. He believes that sacrificing a captured mermaid during a solar eclipse will grant him immortality.
The film uses the historical "Sun King" persona to highlight a central irony: even a ruler who controls the most powerful nation in Europe is ultimately powerless against time.