Kona is a young mermaid who has a thirst for adventure and exploring unknown areas despite the potential danger of being spotted by a human. The thrill of finding something new keeps her going and she never gives up the opportunity for an adventure. One day while exploring another shipwreck, she finds several mysterious objects and encounters the sea fairy Delphi who comes from another world called the Ocean Kingdom. Delphi tells her that the Kingdom was taken over and destroyed because a group of evil, corrupted sirens who have now turned their sights on conquering the human world as well. Delphi tells Kona that she is on a quest given to her by the prince of the Ocean Kingdom to find the legendary warriors known as the Precure as they are the only ones said to have the necessary power to not only protect the human world but to revive the Ocean Kingdom as well. Kona and three humans become the legendary warriors and join Delphi on her quest while discovering themselves and overcoming their own personal issues along the way.

Years after Lun Infinus's mission was completed, a mysterious being takes pity on the five Derelicts, giving them a chance for a better life... ...but when the five get to their destination, they have to learn how to survive among humans that fear them while studying about the life that resides there.