Oona is a mermaid, around Sofia's age, who has blond hair tied in a ponytail. She wears an bright cyan hair comb, with two seahorses on it and decorated with white and pale, light grayish opal colored pearls. Her eyes are moderate vermilion. She has a slender figure, dressed in a vivid cerulean top and a gold tail with light-green fins.
In terms of personality, Oona is very similar to Sofia. Like Sofia, she is a precocious girl who is very clever and unusually serious and mature for a child her age. She is also very kind and loyal to her loved ones to the point of being altruistic. She also values keeping promises no matter what. She also values being self-sufficient to the point where she doesn't like it when people "merbaby" her.
However, unlike Sofia, Oona doesn't suffer from self-esteem issues and lack of self-confidence and is more straightforward and outspoken than Sofia. Also unlike Sofia, Oona is able to stay mad at somebody and hold a grudge with people who have angered her.
Role in the Series
In her debut appearance "The Floating Palace", Oona first meets Sofia when she comes to the surface to take a closer look at the Floating Palace. She accidentally gets caught in a net until Sofia untangles her. The two of them soon become friends, and after Sofia's amulet gives her the power to become a mermaid, they dive into the ocean together.
Oona takes Sofia to her hideaway where they meet Sven and her big sister Cora, who heals her fin. Then, she and Sven give her a tour of the cove. When the Floating Palace appears at the surface and drops anchor, Cora swims up and demands that Oona returns home. Upon arriving, Oona and her mother have a debate on the Floating Palace's presence and discovers Sofia followed her home. Queen Emmaline tells them and Cora about the attack on her Kingdom and that's why they're not supposed to spend too much time at the surface. When Plank proposes that Queen Emmaline move the ship out of the cove with her trident, Oona is against the plan because she knows Sofia's family is on the ship and how devastated her friend will be if they get hurt and can only watch in horror and listen in dismay as all this forces Sofia to admit that she's a human. When Plank starts acting negatively towards Sofia, Oona swims forward and angrily defends her by telling everyone how Sofia helped her when she was hurt and appeals to Cora who only says "All I saw was that you hurt your fin." to Oona's ire. Sven swims forward and says "I saw them. Sofia was helping Oona swim." After Queen Emmaline orders Sofia to leave and never come back, Oona swims away in disgust over how everyone acted toward Sofia and goes after her to comfort her. When Oona catches up to Sofia, she apologizes for how everyone acted and Sofia gives her a loving hug before sadly swimming back to her ship.
On the way back home, Oona is attacked by a sea monster who tries to steal the Mermaid Comb of Merroway Cove from her but fails thanks to the protective charm that's been placed on it. Oona swims back up to the surface and alerts Sofia. The monster captures her and takes her back to a boat and locks her in a cage. His attempts to break the charm protecting her comb draws the attention of Farley the seagull, who was sent by Sofia to find her, who tells Sofia. Sofia tries to save her by herself but the monster is too powerful. Sofia comes back with Cora who saves her with the power of the Mermaid Comb. She later witnesses her mother stop the storm and become friends with Sofia's family, to her delight.
She reappears in the first episode of the third season, "Cool Hand Fluke". She introduces Sofia to all her friends and reveals she's in a band. She plays a variation of a guitar. When her friend Fluke swims off on a dangerous quest, she joins Sofia to help keep Fluke safe. When hiding from the Mantacorn, she expressed her anger and disappointment in Fluke for risking their lives because he was jealous of the attention Sofia was getting. She later forgave him as he was allowed to perform with the band.
Oona makes her third appearance in the twenty forth episode of the forth season "Return to Merroway Cove". She, her family and the other merpeolpe are rehearsing a water show they are going to put on for Sofia and her family who have come to visit again. Sofia shows up and marvels at what they are doing. Oona is a little disappointed because everyone else is doing something big and amazing for the show but she only gets to use her comb to make a few little waves around the fountain that Cora creates. She tells Sofia that her magic Mermaid Comb can do all kinds of amazing things with water but that she's barely allowed to do anything with it. Queen Emmaline tells her that she will teach her more when she's older but Oona insists that she's ready to learn now and swims away in anger. Once alone, Oona laments on how everyone treats her like a little kid and how she can do a lot more than they think through the song "When I Start to Make Some Waves", and uses her comb to create a small sea twister. Onna is successful, but the twister gets to big and swirls away. Onna follows it and soon swims into Sofia. She confesses her mistake and Sofia suggests they tell her mom, but Onna is afraid of the consequences she might face if her mother finds out and convinces Sofia to help her stop it. After freeing Nerissa, they find the twister and Onna tries to use her comb to make it disappear, but instead only makes the twister grow bigger until finally she can't swim against it any more. Luckily Nerissa saves her, but Sofia and Sven get caught up in the twister. While inside, Sofia retrieves Ursula's Necklace from the chest and after Nerissa gets them out, Sofia finally convinces Onna to get her mother. Onna rushes to the castle but only Cora is there. After Sven tells Cora what happen, Cora suggests they use the trident to stop the twister to cover up Onna's deed, but they cannot stop it as every shot they fire at it misses. Then Queen Emmaline arrives and stops the twister with the trident. For their punishment, Onna and Cora are confined to the place for an unspecified amount of time. However, because they told the truth and owned up to their mistakes, Queen Emmaline allows them to take part in the show and their confinement to the place will start the next day.
- Oona becomes the first and only other princess to learn and witness the magic of Sofia's Amulet.
- Oona is the only one Sofia willingly revealed the truth about her amulet to and remembers the truth.
- Like Sofia and her amulet, Oona wears a magical comb which gives her the power to control waves, making her the second princess in the series to possess a magical object.
- Like Ariel, Oona has a secret hideaway where she keeps all her treasures.
- Oona shares the same name with the mermaid character from Nick Jr's Bubble Guppies and a mermaid from a Disney Fairies book.
- Kiernan Shipka and Darcy Rose Byrnes, the voice actors for Oona and Amber respectively, previously worked together on the Nickelodeon show The Legend of Korra voicing the sisters Jinora and Ikki. Ironically, their characters possessed the opposite personalities to both Oona and Amber.
- Coincidentally, both Oona and Jinora are associated with someone with phonetically similar names, Cora and Korra, respectively.