In dying seas, golden- and dark-haired mermaid princesses uncover an ancient entity's engineered corruption perpetuating a 10,000-year doom cycle. Hunted, they confront the mermaid-absorbing Black Queen, uncovering the golden-haired's own dark affinity. Queen destroyed, her parasitic heart infects the dark-haired, revealing their 'victory' is the 47th cycle's failure. Guided by the First Queen, they sacrifice all to break the cycle at the Ocean’s Heart, awakening on land with human legs. Yet, the ocean still dies as stronger, corrupted doubles emerge, whispering of 'her dreams.' An eye opens in the dark-haired's chest; the golden-haired's darkness awakens. Cycle broken, but the true enemy may be the princess beside them; they must discern allies quickly to save their dying world.
