"Happiness Superman League: The Fantasy Mirui Island" is the sixteenth installment in the "Happiness Superman League" series. The Superman League confiscated a prophecy orb, which foretold that the mermaid princess of Mirui Island on Star Planet would turn into foam and vanish, triggering an oceanic crisis on Star Planet. The five superheroes received a mission from the Superman League to travel to the mermaid tribe on Mirui Island and prevent the prophecy from coming true. Unexpectedly, the magician Lehehe still managed to steal the mermaid princess's song, causing her to turn into foam. The superheroes failed to stop the prophecy from unfolding. In the end, the unwavering superheroes joined forces to defeat Lehehe, rescued the mermaid princess who had turned into foam, and simultaneously saved the ocean world.