Bia is the Abysmal Princess, responsible for maintaining order and taking care of the throne as ruler of the Abysmal Kingdom while her parents are travelling throughout the kingdom. As such, she is known as one of the more "precocious" princesses. She is also known as one of the most beloved princesses at school, but unlike the other princesses, she has private classes with Miss Marla at night because the daylight is too bright for her.
Bia has a lock of red hair and paler skin compared to the other princes and princesses because very little light reaches the Abysmal Kingdom. She also wears a white dress along with a crown modelled on an anglerfish and carries a lantern on a staff. In the animated series, Bia can put on a big, bossy voice, which can scare Salacians when they hear her. She has a pet pelican eel named Slipper, who can transport her around the Abysmal Kingdom.
Many Salacians were afraid of Bia because they believed that the Abysmal Kingdom was haunted, but as some princesses and princes, such as Polvina, Ester and Tubarina, got to know her, they realised that Bia is actually a friendly princess who enjoys the company of others.
In The Toy, Bia meets the girls for the first time as they swim down into the Abysmal Kingdom to ask the Abysmal King and Queen about some writing on a card that Polvina found in a box with a small toy octopus. Though the girls were unable to speak to the Abysmal King and Queen, Bia is able to translate the card, which was written in the ancient language of the Abysmal Kingdom, before taking the girls back up to Salacia with Slipper.
In The Big Game, Bia encounters Ester and Maurico when they head down to the Abysmal Kingdom to retrieve a flubberball that fell there, only for it to be eaten by an anglerfish. After briefly scaring Maurico with her appearance, Bia introduces herself to him before she goes to separate a pair of giant squids (again), who are slinging mud at each other over "nothing much". Ester and Maurico use their flubberball sticks to deflect the mud back at them, pacifying the fight before Bia and Slipper take them back up.
In Rumours, Bia sends Slipper with a letter to the girls, saying that she will be coming to visit them soon. When Marli and Vivi overhear this, they and a few other princes and princesses relay to each other some rumours they heard about the Abysmal Kingdom, such as that everyone from there has six arms, big eyes, lights on their head and huge fangs that "eat absolutely anything". After the girls fail to convince the other princes and princesses that Bia is not what she seems, they set up an elaborate scheme with Bia and Slipper to do so. First, the girls plan a party for Bia, but they don’t invite the others in the hope that they will crash it. Next, the girls dress up as "Bia" while the others sneak up to the ballroom in a cage. When "Bia" and Slipper confront them, Slipper flips the cage over and everyone flees. As they pass by the actual Bia, who was hiding this whole time, she leads them into a room and briefly introduces herself before going out to confront "Bia". Eventually, Bia and the girls are unable to keep up the act and they reveal their act to the others, successfully convincing the other princes and princesses that she is just like them.
When the girls believe that Ester's grandmother fell into the Abysmal Kingdom in The Runaway Grandmother, they head down in search for her, only to be chased by an anglerfish. They later meet Bia on the way to the Abysmal Palace and ask her whether they saw Ester's grandmother, but neither she nor the anglerfish have. Bia and the anglerfish take the girls back home, where Ester's grandmother was revealed to have been at the Starfish Palace all along.
When giant starfish from the Ice Oceans take over the Abysmal Palace in The Giant Starfish, Bia goes up to Salacia and asks the girls for their help. Upon meeting Ester, the starfish make her their queen, but when she tells them that she has to return to Salacia, the girls learn that they want to take over Salacia as well. The girls hide inside the palace, but when they try to break the door down, they hide under a rug behind Slipper in an attempt to get past the starfish, but they are discovered. Polvina has Ester lead the starfish up to Salacia, but when they get up there, they are unable to withstand the light and warmth, so Ester commands them to return to the Ice Oceans.
In The Scare, the girls attempt to lure Marcello down to the Abysmal Kingdom after he says that girls are easily frightened compared to boys. Sure enough, Marcello is frightened by everything he sees, but when Bia confronts him after he says that the Abysmal Kingdom, he swims away. Bia goes with the girls as they try to find him; Bia deduces that he is with a couple of baby eels given that he was wearing an eel costume. Eventually, when they do find him, Marcello and the baby eels deny that they got scared, but sure enough, Marcello gets scared again upon seeing Slipper. The girls invite Bia back to the Shark Palace to join them on their sleepover.
In The Last One, the girls come to the aid of a lone goblin shark in the Abysmal Kingdom, who became lost and was calling out for a friend. They take the shark to Bia at the Abysmal Palace, where they find out what the shark is. As Bia sends Slipper and his family to find any other goblin sharks, the girls decide to narrow down the search by asking the goblin shark about his mother. Sure enough, he remembers her, but he lost her before he saw a monster the size of a reef. Bia realises that the shark is referring to Monster Reef and the girls take him there. The shark tries calling out again, but after a few failed attempts, they hear a response coming from a cave inside the monster’s mouth. The girls head in and they find the goblin shark’s mother and family.
In the books
Bia makes her book debut in The Windy Letters. Bia encounters Polvina when she was forced to separate from her friends upon heading into the Abysmal Kingdom. Blinded by the light of Polvina's torch, Bia asks her to put it down as she is joined by Ester, Tubarina and Mr Gilson. They learn that Mr Chain and Weasel had taken Tata hostage, so Bia instructs Polvina to keep Mr Chain talking on the phone while Mr Gilson leads them to their hiding place. Once they get close enough, Bia confronts the two bandits before setting the abysmal fish upon them and tying them up.
Bia proceeds to invite the girls to her palace for dinner; she and her butler, Romero, are the only ones living there as her parents are currently out looking for food for the abysmal fish. When Tubarina bluntly asks Bia why she can live in such a dark place, she tells her that it is her home and that it is her mission to take care of the abysmal fish. Bia then asks the girls what brought them to the Abysmal Kingdom and Tata tells them about their adventure and quest to find the third letter from a Drylander girl named Windy. Bia says that she hasn't heard of it, but she will have the abysmal fish keep a look out for it. The girls and Mr Gilson then leave for home, taking Mr Chain and Weasel with them.
Soon after, a dragonfish found the bottle with third letter just as it was about to eat it. It was passed on to Bia, who then passed it on to Miss Marla during her night class. Miss Marla would then have it translated for the girls and Tata the next day.
Before the events of The Ballad of the Forgotten Princess, Thorn, a minister of the Abysmal Kingdom and a friend of Bia's parents, overthrew them, forged their disappearance and became the new Abysmal King, calling himself the Shadow King. At risk of danger due to being heir of the throne and with no evidence to incriminate Thorn, Bia desperately went to Polvina for help. Bia used her lantern, which is actually an ancient Salacian artefact known as the Staff of Oblivion, to make everyone forget about her, with Polvina writing a ballad with clues to Bia's true identity so that she could find her in case something went wrong, thus making her the "Forgotten Princess". Bia then proceeded to hide the Staff of Oblivion in a rock safe within a secret chamber in the Abysmal Palace before going into hiding.
Bia later resurfaced in disguise as Maya, an outspoken yet sombre civilian girl, making her home in the hull of a wrecked Drylander carriage. Late at night, she visits Polvina at the Octopus Palace to warn her of spies. Upon being shown the ballad, Maya covertly takes it and presents it to Thorn in order to gain his trust.
Returning to the Octopus Palace the next day to return the ballad, Maya is asked by Polvina to tell her about herself, but she manages to change the subject to make it about Polvina. She is almost brought to tears when she sees a picture of Polvina's parents, but she brings herself together and prepares to leave, but not before Polvina gives her a pink blouse to replace her hooded top.
The next day, Thorn orders Maya to steal the royal family records from the Grand Library of Salacia. That night, before she does so, she goes back to the Octopus Palace, only to find Ester and Tubarina with Polvina. While the girls tell her what they learnt about the Staff of Oblivion, Maya offends the girls by calling them "snobs". When Tubarina offends her back by rudely asking her to help them solve their mystery, Maya decides to leave, saddened at the fact that she couldn't be like them and live in peace.
After stealing the royal family records and ransacking the library, Maya brings the records back to Thorn. Thorn has Maya captured after seeing the Abysmal Royal Family's records absent and realising Maya's true identity as the Forgotten Princess, namely Bia. The Shark King and Miss Marla arrive to confront Thorn, at which point Bia offers to hand the Staff of Oblivion over to him. Despite a small accident involving Polvina and Ester, Thorn proceeds to use the Staff of Oblivion to make everyone recognise him as the true King of Salacia, only for it to backfire on him due to him not being the Staff's guardian.
While Bia is freed, Miss Marla takes the Staff of Oblivion from Thorn and gives it to Bia, who then proceeds to use it to make everyone remember her again. Thorn's crimes and accomplices were exposed thanks to Bia, Polvina and Miss Marla's plan. Though she initially thought she would have to live without her parents, Bia's concerns were alleviated when they were found in the cave where Thorn had held them prisoner.
At the end of the year, Bia travelled with Polvina, Ester and Tubarina throughout the Abysmal Kingdom, visiting children like Maya and having adventures. Miss Marla would also write new verses to the ballad to ensure that Bia's story would be remembered for generations to come.
In The Monster from the Bottom of the Sea, Bia is waiting for Polvina to visit when Draco appears and alerts her to a monster in the Abysmal Kingdom, scaring all the abysmal fish. After finding Polvina's backpack, Bia and Draco are apparently confronted by the monster, but Bia realises that it is actually Polvina, who had gotten lost on her way to the Abysmal Palace. After clearing everything up, the three head to the Abysmal Palace together.
- In The Toy, Bia states that she does her schoolwork at home and that Miss Marla visits her once a month, which slightly contradicts the description given in the character details. This implies that she does not go to the same school as the other princes and princesses.
- In Stage Fright, duplicates of Bia are shown in the audience during the performance. Though the duplicates of her and some other characters can be interpreted to represent random people, Bia's appearance in that episode would contradict her depiction in Rumours if taken at face value.
- It can be inferred that Bia was seen during the performance but since she is not seen interacting with anyone else in the episode, nobody knows who she is, justifying her depiction in Rumours where she is introduced to the others for the first time.
- As stated in The Ballad of the Forgotten Princess, the name Maya stands for "illusion" in the Sanskrit language.