Marina takes the viewer on the fairytale adventures of the mermaid Marina. Born as Cristina to human parents Esther and Elias, Marina falls victim to a curse by Victoria, a sea deity disguised as a normal woman. Seeking vengeance on Elias, who spurned her love and married Esther, Victoria cursed their daughter. In the hopes that Victoria would lift her curse on the child, Elias leaves Esther but eventually falls into insanity. Esther, on the other hand, was left to raise Cristina alone. When the curse came true and the child turned into a mermaid on her seventh birthday, Esther realized that Cristina's life would be endangered in their superstitious fishing village, where mermaids are believed to be unlucky. As such, Esther is forced to release Cristina in the sea, where she is found and cared for by the mermaids headed by Istah, their beauteous queen.
With the heart and mind of a human being, Cristina, now also known among the mermaids as Marina, dreams of nothing else but to walk again and live the life that was taken away from her. This is only possible through the sea witch Dugong. Marina seeks the help of Istah, who gives her a precious necklace to be offered to Dugong in exchange for her legs.
Marina became human again and returns to land to claim everything she has lost. However, she soon discovered that when the moon is full, she becomes a mermaid again and that only true love's first kiss can free her from the curse. Dugong, on the other hand, learned that the powerful necklace of Istah was a trap. Donning the necklace, she discovered that she cannot remove it and, worse, suffers the same injuries Marina does.
Meanwhile, Dugong's mother and Victoria's aunt, Tandang Ella, pays a visit to Victoria. She trades the power of the Aram for a chance to see her daughter again. Dugong, having been separated from her mother since she was an egg, harbored ill-feelings but, upon learning that her mother is alive and is looking for her, could not help looking forward to meeting her mother. Victoria, however, tricks the old woman and kills her the moment she met her daughter, believing Dugong hated her mother anyway. She kept the power of the Aram for herself.
On the eve of Marina's 21st birthday, Victoria and her daughter Luna paid a surprise visit to give her stepdaughter her "gift". Using the powers of the Aram, she turned Marina back into a mermaid. Victoria then went to a circus where she made the poor mermaid the star attraction. When the circus master wanted more oddities to star in the circus, Victoria also used the powers of the Aram to capture Dugong and her slave, Pearly.
Rodge attempted to rescue her love but Luna had placed him under a curse, turning him into a kitten. Eventually, with the help of her newfound friends, Marina was able to get away from Victoria's clutches and eventually found her way into another fishing town, to a family of fairies.
The King of the Seas ordered to have Victoria and Luna arrested and placed inside a force field prison for them not to get away. Marina, on the other hand was now able to live her life as a human when she married Rodge and was now pregnant.
All things seems well except for Victoria. She wants to give revenge to the people who foiled her evil plans. She had heard of a meteorite stone that, once in the hands of its owner, can give out an enormous power. She escaped from her prison and got her hands on one of the stones that fell that night. By using its power, the evil witch had Luna and Marina switch places, with the latter's unborn child now under Luna's womb.
One day, Marina woke up and found herself inside a prison and the shokoy guards calling her "Luna". She eventually come into conclusion that Victoria will not rest unless she gets her way. By the help of many of her friends who see her as Marina beyond what they physically see, they were able to break Victoria's spell, although Marina's child was still inside Luna's womb (in later episode, Luna gave birth to Marina and Rodge's baby girl who was later named Mariluna and seems to be inheriting Marina's curse).
Victoria still won't give up, that's why she had Marina killed but on the cost of her life. Marina's mother, Esther began having dreams for which Marina is talking to her to get the Leafar, a magical liquid that can resurrect the dead. But Victoria was able to get into the gate connecting the world of the afterlife and the world of living, standing Marina in between. Esther was surprise to see that who she had resurrected was not her daughter but the ever evil witch.
Marina, lost bin between the two worlds got help from her father, who is now a spirit. The only way to revive herself again to finally defeat Victoria was to return herself into mermaid once more.
Eventually, she was able to defeat Victoria but the cost of it, her last chance of being human forever. She gave her child under the care of Luna and told her to take care of her child as well as her husband, Rodge. Marina, now forever a mermaid for eternity, bid goodbye to Rodge and their child and returned once more into the ocean.
- Aram - a sentient stone with an orange glow kept in a small chest, this originally belonged to Tandang Ella. It was given to Victoria in exchange for helping the old witch find her daughter Dugong. It is capable of tapping into the power of the Earth or sealing other people within itself, among other things. It was eventually obliterated by Tandang Ella, who destroyed it from the inside when Victoria sealed her and Dugong within.
- Latigo ni Luna - a whip bestowed by the Aram to Luna, it contains part of the Aram's power.
- Leafar - a liquid that can resurrect the dead.
- Batong Bignoy - a greenish crystal ball that shows events, very much like a television, only, it has no sound. It has been used by Istah and, later on, Dugong.
- Batong Malo - Initially implanted in the eyes of Shiela, this gives its host the ability to fire beams of white light through their eyes, though these beams are fatal only to Dugong. It is also capable of increasing the amount of Samared stones a person may have.
- Kwintas ni Istah - A necklace that originally belonged to Istah. When it was worn by Dugong, it also served as a bond to Marina; whatever injury Marina suffers is also reflected in Dugong. It is a collection of stones, each with a peculiar power. The stones below were originally part of the necklace.
- Batong Samared - marble-sized stones that emit a green glow. It can grant wishes, allow its wielder to access the power of the seas and is capable of erecting dome-like shields. It is the only stone that can stand up to the power of the Aram.
- Batong Okyet - it has the power to turn a person into a mermaid.
- Bituing Kasang-alam - a fragment of a falling star, it has the power to grant almost all of its owner's wishes unlimitedly. After the Aram was destroyed, Victoria got one half of it, which can only be used for evil while Marina got the other half from Dugong's long lost sister: the half that was meant to be used only for good. Like the Aram, it is also sentient.