Cleao Everlasting is the youngest daughter of the Everlasting noble family, recognizable by her long blonde hair and blue eyes. Initially sheltered, she possesses a carefree, teasing personality underpinned by bravery, frequently clashing with Orphen due to her stubbornness and refusal to admit fault. Despite her noble status, she exhibits athleticism and fencing skills honed at boarding school, enabling her to effectively wield the Sword of Baltanders. This sword, inherited from her late father, becomes central to her journey when Orphen seeks it to cure his sister Azalie.

Her involvement with Orphen began a year prior to the main events when she observed him watching her family's mansion during a moonlight swim, sparking fascination. After returning from boarding school, she discovered him watching the mansion again, later realizing his true interest was the sword. When the dragon Bloody August attacked her home to claim the sword, Orphen intervened and revealed its significance. Amidst the chaos, the sword was stolen, prompting Cleao to stow away with Orphen and his apprentice Majic to recover it, citing her duty to protect her inheritance.

Her motivations for joining the journey extended beyond the sword; she sought to understand Orphen's enigmatic personality, driven by lingering admiration from their first encounter and genuine compassion for his mission to save Azalie. Over time, she transitioned from a brash, self-centered noble into a devoted companion, openly supporting Orphen and developing empathy for Azalie's plight. Her relationship with Orphen evolved into a partnership, balancing his tendencies with her pragmatic interventions.

Cleao exhibits latent magical potential, unconsciously channeling magic through Leki, a Deep Dragon cub she adopted. Leki's presence enhances her abilities, and their psychic connection later unlocks her full magical capacity. She trained under Leticia to develop these skills, achieving proficiency within a year. Her combat abilities include swordsmanship and firearms training received at the Tower of Fang.

Across her journey, Cleao matured from a sheltered teenager into a resilient adventurer. Her bond with Orphen deepened, culminating in marriage. They settled on the Hara continent, had three daughters—Ratsbane, Edge, and Ratchet—and established the Swedenborge School of Sorcery. Her legacy involves reconciling her noble roots with a life dedicated to magic and family, marking an arc from a curious observer to a foundational figure in Orphen's world.

Name variations exist across media, with "Claiomh Everlasting" used in light novels and "Cleao Everlasting" in anime adaptations, both referring to the same character.