Nerissa appears in the episode "Return to Merroway Cove." When Sofia swims into a cave and gets startled by a Scare-Acuda, Nerissa arrives and grabs him with her Enchantlet. Nerissa recognizes Sofia as Chrysta's Protector trainee and tells Sofia that she and Chrysta trained to be Protectors together. After Nerissa sends the Scare-Acuda to the north end of the cove, she explains to Sofia that she's come to Merroway Cove to find Ursula's Necklace, one of the Wicked Nine which is hidden in a Kelp Forest, and take it to the Mystic Isles for safe keeping.
Nerissa leaves, heading to the hiding place of the Wicked Nine object she is searching for. But along the way, she sees a young octopus named Octavio caught up in the sea twister created by Oona. Nerissa pulls him free, but she gets caught up in the twister herself. Octavio tries grab her, but pulls off her Enchantlet. Sofia, Oona, Sven, and Octavio find Nerissa trapped underneath the fallen mast of the Stormy Shipwreck where the sea twister went. Knowing her Enchantlet alone would not be strong enough to free her, Sofia bonds hers and Nerissa's Enchanlets together and successfully lifts the mast off Nerissa's tail. After Nerissa is freed, she tells Sofia that Ursula's necklace was in a chest buried under the shipwreck but the twister took the chest with it. When they find the twister, Oona tries to make it go away with her Mermaid Comb, but that only leads to the twister growing in size until Oona cannot swim against the current anymore. Nerissa saves her but Sofia and Sven get pulled into the twister. The Princess manages to swim into the eye of the twister where the chest is and the water is calmer. Sofia retrieves Ursula's Necklace from the chest but she and Sven are unable to get out of the twister. Nerissa pulls them out by binding the Enchantlets again. Then they notice that the twister is heading toward the palace. Oona rushes to get her mother while Nerissa and Sofia try to slow the twister down.
They attempt to stop it by causing a mountain of big rocks to fall in its path but it doesn't work. Suddenly, Queen Emmaline arrives and stops the twister with her Trident. Nerissa thanks Sofia for helping her get Ursula's necklace and tells her that she's going to make a great Protector, then takes the necklace back to the Mystic Isles.