Ella, a modern fitness influencer, time-travels and inhabits the body of the third mermaid princess. Weighing 400 pounds, she is scorned by the royal family and constantly humiliated by her elder sister Vivian and the villainous Damon. The original princess stole the purple pearl that Lance, her partner, gained at the cost of great danger to please Damon, leaving Lance burdened with her debts. After taking possession of the body, Ella awakens to reality. She applies her professional fitness knowledge to cut sugar and salt intake, reduce edema and train her core, gradually transforming from an overweight mermaid into a slender and graceful one. She establishes the White Coral Beauty Salon and the Silver Scale Academy to help merfolk of all ranks reshape their figures. While running her businesses to settle debts, she thwarts the plots of Vivian and Damon and investigates a three-year-old wrongful case that cost Lance his knighthood. Lance, reserved and affectionate, initially intends to terminate their partnership contract. However, he falls in love with the changed Ella as they fight side by side. They endure poisoning, the trial of Siren’s Tears, pursuit from Arnold and a dramatic showdown at the Neptune Festival. The injustice is eventually overturned, and Lance recovers his honor. The two dissolve their original contract and enter a new voluntary bond. As the pioneer of deep-sea body shaping, Ella joins Lance to run the Silver Scale Academy and protect the undersea world.
