Lia is the Lionfish Princess. While the lionfish are shy and do not like to chat, instead tending to live hiding in the rocks and corals, Lia is not like them. A talkative girl who "speaks by the elbows", Lia cannot stand staying inside her palace for a long time; she loves going to birthday parties, the movies or her friends' houses.

In The Diary, Lia discovers that a solefish took her red pencils. It is later revealed that a Mimic Octopus disguising himself as a solefish was the one who took them, along with other red items.

In The Missing Princess, Polvina is worried about Lia as they had agreed to meet the day before, only for the latter to not turn up. When she, Ester and Tubarina go to the Lionfish Palace, they find the Shark King coordinating the search for Lia, who is revealed to have gone missing. They proceed to search her room, where they find her bag and some of her clothes missing. After leaving the palace, the girls attempt to ask a couple of lionfish about Lia's whereabouts only for them to rudely swim off, leading them to believe that they know something. Polvina enlists the help of the Mimic Octopus, who disguises himself as a lionfish as he follows two lionfish to a cave where they are sneaking food. After reporting back to Polvina, he takes her and the girls to the cave where they find Lia, who has run away because she cannot bring herself to make a speech to the lionfish elders out of embarrassment. Ester decides to convince Lia to make her speech by taunting two lionfish sneaking food to her, but instead of summoning the elders as Ester expected, the lionfish gather their friends and trap the girls in a cave. The Mimic Octopus manages to sneak away and get help from Lia, who arrives just as the girls plan to rush through the lionfishes' poisonous fins. After Lia rectifies the situation with her friends, the girls convince her to make the speech to the lionfish elders, which she eventually does after some coaxing. Following this, Lia decides to practice her speaking so she can give some talks to young lionfish about "always telling your parents where you're going and not making them worry".

Lia is 7 years old and has the sign of Leo (♌).