Oona is a mermaid, around Sofia's age, who has blond hair tied in a ponytail. She wears an aqua colored hair comb, with two seahorses on it and decorated with white and aqua pearls. Her eyes are amber brown. She has a slender figure, dressed in a cyan top and a gold tail with light-green fins.
In terms of personality, Oona is very similar to Sofia. Like Sofia, Oona 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 accidently 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 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 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.