Princesse Leona is a central character in Dragon Quest: Dai no Daibōken, serving as the princess of the Kingdom of Papnica and one of the Disciples of Avan. She is introduced as a fourteen-year-old royal who travels to Dermline Island to undergo a ritual meant to make her a full-fledged sage. Papnica is a land renowned for producing powerful mages, and Leona has been trained in magic from an early age, though she is still regarded as a sage in training rather than a completed one. Her first meeting with Dai is marked by mutual poor impressions, as she bluntly dismisses him as small and unreliable, while he finds her sharp-tongued and harsh. Despite this awkward start, the two grow close, and Leona becomes Dai's first human friend. During the island incident, when a scorpion's poison threatens her life, Dai awakens his Dragon Knight power to save her, and Leona develops deep trust and affection for him, promising to meet again once he becomes a true hero.

In terms of personality, Leona is highly energetic, outspoken, and fearless, unafraid to state her opinions directly even to those older or more powerful than herself. Her frankness can come across as severe, as noted by Dai, who describes her as cute but not particularly demure and as having a sharper temperament than Maam. Yet her honesty is also what endears her to her companions, who appreciate that she speaks her mind without hiding her thoughts. She possesses a strong sense of duty and a clear distinction between her public and private selves, using a formal first-person pronoun in royal or official settings and a casual one among close friends. Though she acts in ways that sometimes seem unprincesslike, such as joining festive drinking and dressing practically or playfully, she is fully aware of her responsibilities and conducts herself with dignity when the situation demands it. She is also shown to be curious about romance among her companions, displaying an ordinary teenage girl's interest in such matters.

Leona's motivations are rooted in protecting her kingdom and its people and in proving that the values she has inherited are correct. After the Demon King's forces return, the Undead Legion under Hyunckel destroys Papnica, and her father the king goes missing and is later confirmed dead. At a very young age, she effectively becomes the leader of her nation, sheltering with her remaining retainers and waiting for rescue while maintaining hope that Dai will come for her as he once did. When she finally faces Hyunckel, the man who brought ruin to her country and her family, she chooses not to punish him out of personal vengeance. Instead, she forgives him and charges him to dedicate his life to fighting as a true Disciple of Avan, a decision that demonstrates her wisdom, magnanimity, and political insight, and that earns even the grudging respect of the veteran mage Matrif.

Leona's role in the story evolves from a princess in need of rescue to a leader, a supporter, and ultimately a legitimate member of the heroes' party. She initially serves as the group's healer and support caster after Maam leaves to train as a martial artist, and her healing magic becomes vital in difficult battles. Later she departs the frontline to organize a summit of the world's kings, building unity among humans against the Demon King's forces. Near the end of the story, guided by Queen Flora of Carl, she joins the resistance and becomes the fifth Disciple of Avan, inheriting Avan's mark and receiving recognition directly from Avan himself. She then undergoes trials to learn the grand spell Minakator, which she uses in the final battle to disable the enemy stronghold and allow her comrades to advance.

Her key relationships are centered on Dai, Popp, Maam, Hyunckel, and Flora. With Dai, she shares a deep bond that carries romantic undertones; she serves as his emotional anchor, encouraging him when he is paralyzed by fear and even striking the great demon lord Vearn with a knife to inspire the party. Although the two never openly confess their feelings, their mutual affection is clear, and after Dai disappears at the end of the war, Leona remains steadfast in her belief that he will one day return. With Popp and Maam, she is a loyal companion who speaks candidly to them about their weaknesses. With Hyunckel, she transforms from an enemy into a gracious sovereign who grants him a path to redemption. Queen Flora is her most respected figure, a model of leadership whose path Leona mirrors when she too rises to guide a kingdom in crisis.

In terms of abilities, Leona is proficient in both fire and ice spells, as well as other offensive and utility magic, but her greatest strength lies in healing. She is the party's primary user of Behoma for much of the story, and she also learns revival magic, though her attempts at it are not always successful. She has no extraordinary physical power and rarely fights directly with weapons, but her intelligence, leadership, and courage are considerable. Her most significant achievement is mastering Minakator, a powerful sealing spell that requires passing a spiritual trial, through which she proves her conviction that the justice she inherited is genuine. Along with the magical feathers given to her by Avan, she becomes an indispensable support for the party despite her relatively limited direct combat role.

Throughout the series, Leona develops from a proud and somewhat spoiled princess into a compassionate and capable ruler, a proven warrior of the heart, and a trusted comrade who helps carry her friends through their darkest moments. Her defining traits are her sharp tongue, her unwavering resolve, her generosity toward those who have wronged her, and her deep, patient love for Dai.