Marina is a mermaid who is in love with Prince Justin, a human prince from a kingdom on the shore. Marina saves Justin when he almost drowns after a chase from a giant Cyclops and a shipwreck attack from a three-headed sea serpent. She then makes a deal with Hedwig the sea witch to become human temporarily to try to win Justin's love. Justin and Marina become close but Justin thinks that Princess Cecily, a human princess, was the one who saved him from drowning and therefore he gets engaged to her. Justin eventually remembers that Marina was the one who saved his life but by then Marina becomes a mermaid again. The two continue to secretly meet and try to find a way to be together while dealing with Hedwig's plans to take over the kingdom and Cecily's attempts to get Justin to marry her. Marina and Justin are aided by their underwater friends Winnie the seahorse, Bobo the tropical fish, and Ridley the sea otter. They are also aided by the wizard Anselm and by Chauncey, Justin's page.
Characters
Main characters
Marina : A mermaid with waist-length golden blonde hair and green tail who is the protagonist of the show. After she saves Prince Justin of Gandor she falls in love with him and wishes to become human.
Prince Justin : Prince of Gandor and Marina's boyfriend.
Winnie : Marina's seahorse friend and constant companion. Unlike real world seahorses, she has the ability to scream at very high pitches which causes people to pass out. She also has the ability to fly when she is out of water.
Bobo : Marina's tropical fish friend. He often spies on Hedwig and reports back to Marina and the rest of the gang.
Ridley : Marina's sea otter friend and Anselm's companion. Unlike real world sea otters, he seems to be able to breathe under water indefinitely.
Anselm : Prince Justin's tutor and secretly a sorcerer who was once in love with Hedwig in their youth.
Chauncey : Prince Justin's short, goofy and loyal page.
Antagonists
Hedwig the Sea Witch : The sea witch who acts as the main antagonist of the show. She was once a sorceress who was in love with Anselm until her hunger for power forced him to banish her to the sea. She comes up with plot after plot to capture Marina and Justin so she can exchange them for the Amulet of Power which would make her the most powerful person on both land and water and therefore rule the world. Just like a mermaid, she doesn't have legs and her tail resembles that of a moray eel. The power that she uses most often is to release prehensile vines from her long fingernails.
* Dudley : Hedwig's halfwitted scalloped hammerhead shark second-in-command. His role is a lot more prominent than the other henchmen of Hedwig and he serves as the comic relief among the antagonists.
* Ray: Hedwig's manta ray. He acts as her means of transport and spy. He is heard speaking sometimes but other times he is shown to only be able to mumble. It's not clear what his name is as Hedwig once calls him Ray and another time she calls him Manta.
Cecily: A mean aristocratic girl who likes Prince Justin even though he doesn't reciprocate her feelings. She was his promised bride before he met Marina. Her father is Lord Ainsworth.
Prince Lothar : Prince of Brakston and Justin's sworn enemy. He often cooperates with Hedwig.
Secondary and minor characters
Barnabas: Marina's younger brother. He is a very good inventor and his tail is blue.
Coral: Marina's bossy older sister. Her tail is pink.
King Nestor: King of the world's oceans. King Nestor is extremely strong as can be seen when he easily beats Hugo with his bare hands. His tail is dark blue.
Marina's grandmother: She lives in the same castle as Marina. She is seen briefly in two episodes and her voice can be heard in another one.
King Charles : Prince Justin's father.
Queen Catherine : Prince Justin's mother. She is very interested in her son's love life and tries to act as his matchmaker.
Orcus: A whale who helps Marina and her friends a few times.
The series uses two pieces of theme music for the original Japanese version. The opening theme is called "Yumemiru Mermaid " and the ending theme is called "Pearl-no Kimochi ", both by vocalist Yumi Hiroki, who also portrayed the voice of Winnie in the Japanese version of the show. Rachelle Cano performs the theme music for the English dub version. Music from the English version was used for the English dub of Digimon Adventure.
