Isa is the Penguin Princess. She is the only student from the school who does not live underwater; instead, she lives in the Penguin Kingdom in the South Pole (which is considered to be between Salacia and Dryland). Isa was afraid of water, but with the help of Santa Claus, she overcame her fear and today she fondly wears a small Santa hat on her crown.

The origin of Isa's Santa hat and initial fear of water is elaborated in the short story Isa's Gift. During class, Isa finds herself unable to explain what she intends to do with her hat as it is a tradition in Salacia at Christmas for families to give the presents they received the year before to others. Later, she explains to Polvina, Tubarina and Ester about the origin of her hat; since Isa was born out of the water, she was too afraid to get into it, even though her penguin friends have been swimming their entire lives. On Christmas the year before, Isa got a magical Santa hat and when she put it on her crown, her fear of water was gone, but she cannot take off her hat otherwise she would drown and die. Upon hearing the story, Tubarina and Ester begin fighting over her hat, causing it to be ripped. Seeing this, Isa began to choke. A few minutes later, she recovers and discovers that she is able to breathe underwater without her hat, proving that all she needed was a little bit of courage. The next day in class, Isa tells everyone that she intends to give her torn hat to a penguin named Mr Penpen and that she wants another Santa hat this Christmas so she can remind herself that she has the courage to swim and live in the water.

Isa is 6 years old and has the sign of Scorpio (♏).

Isa is voiced in English by Di Adams.