Fine is one of the two twin princesses of the Sunny Kingdom and a main protagonist. She has red hair and red eyes, traits she inherited from her mother, Queen Elsa. She is often described as one of the most unprincess-like princesses in the history of the Mysterious Planet. In the sequel series, she and her sister are sent to a Princess School to earn the certification needed to become queens, where they gain new transformation abilities.

Fine has a bright and warm-hearted personality, remaining cheerful and optimistic in most situations. She is friendly, kind, and deeply cares for her friends, family, and the people she loves. Her athletic ability is one of her strengths, though dancing is a notable weakness for her. Fine is also quite gluttonous, with her attention often turning to food, especially cake, whenever she attends parties or events. Unlike her more composed sister Rein, Fine is easily frightened, particularly by ghosts and other supernatural things. Despite often being slow to understand what others are thinking, she is always eager to help her friends and tries to cheer people up even when she does not fully understand a situation.

Her primary motivation is to save the Mysterious Planet, as the central sun that illuminates all seven kingdoms is weakening. Along with her sister, she has been gifted with a magic known as the Prominence, which they use in their quest to restore the sun's power. She does not mind losing the formal Princess Parties so long as she can make those around her proud.

Key relationships define much of her journey. Her bond with her twin sister Rein is the most important, as they must work together to use their most powerful magic and support each other constantly. Fine, along with Shade, is one of the only characters who can understand Shade's little sister Milky when she speaks, a connection Poomo suggests is due to their shared love of eating.

Her most significant relationship develops with Shade, the prince of the Moon Kingdom who initially appears under the alias Eclipse. Fine was the first person to trust Eclipse, believing he was not as bad as everyone thought, which eventually leads her to fall in love with him. This contrasts with her feelings toward Prince Bright, who admires her, as she shows no interest in him during the first series. Later in the first anime, as she and Shade get to know each other better, she becomes his love interest, a connection that continues into the second season. She shows occasional jealousy in situations where Shade pays more attention to Rein.

Throughout the story, Fine grows from a somewhat naive and easily frightened princess into a more confident individual. While she sometimes becomes too scared to act, she can quickly overcome her fear when her sister is in danger, demonstrating how much she cares for Rein. Her ability to see the good in someone like Shade, when others could not, marks a significant development in her character, as she learns to trust her own judgment and emotions.

In terms of abilities, Fine possesses the magic called Prominence, which she uses alongside her sister to solve problems and help the inhabitants of the various kingdoms. She and Rein require each other to transform and to use their most powerful magic. In the sequel series, their powers expand as they gain the ability to transform into their Universal Princess forms with the help of their twin angel mascots, Pyupyu and Kyukyu. The Feather Myuugram is another magical item that can be used to make targets dance uncontrollably. Despite her magical capabilities, her practical skills have limits, as she possesses terrible cooking skills.