Aria Governess serves as the chief maid, great chamberlain, and personal escort to Liselotte Cretia, holding the position as the most trusted aide and the strongest among all of her retainers. Born as the daughter of a viscount in the Kingdom of Beltrum, her early life was one of nobility and privilege. During her time at the Beltrum Royal Academy, she was a classmate of the brilliant mage Celia Claire, and the two became best friends. While Celia was unrivaled in the field of magic, Aria established herself as the most skilled swordswoman of her generation, with no male student able to stand as her equal.

This life changed dramatically at the beginning of her sixth year at the academy when her family fell from nobility and faced ruin. Forced to leave her studies, Aria took up a position as a maid in the royal castle of Beltrum. It was during this period that she was assigned to attend to Rio, also known as Amakawa Haruto, during his stay at the castle before his audience with the king. Together with Celia, she helped teach him the necessary etiquette for the royal audience. However, the environment at the castle proved to be difficult, and she suffered incessant harassment from her coworkers due to her status as a fallen noble. Unable to endure this treatment any longer, she resigned from her post and chose to become an adventurer.

Aria's career as an adventurer lasted for approximately four years, and her prowess in combat quickly became well-known, earning her the fearsome nickname of the Reaping Princess. Her exceptional abilities eventually caught the attention of Liselotte Cretia, who was still studying at the Galarc Royal Academy at the time. Recognizing Aria's potential, Liselotte scouted her and brought her into her service shortly after her own graduation. This decision proved to be a pivotal moment for Aria, as she found in Liselotte not only a master but a trusted confidante with whom she formed a deep and unshakable bond. The trust between them is so profound that Liselotte even revealed to Aria the secret of her past life as a reincarnator, a fact she has not disclosed to her own parents.

In terms of personality, Aria is known for her calm, caring, and responsible nature. She is deeply sincere, trustworthy, and approaches both mundane domestic duties and dangerous combat missions with equal diligence and a strong sense of duty. Her resilience in the face of adversity, from her family's downfall to the harassment she endured, speaks to a core of inner strength. She carries herself with the grace and intelligence befitting her noble origins, yet she has fully adapted to her role as a servant, finding purpose and loyalty in her service to Liselotte.

Aria is a formidable warrior, and her combat skills set her far apart from her peers among the maids. While she is also competent in magic, able to trigger her spells more quickly than the average mage, her true expertise lies in swordsmanship. She is the wielder of a powerful magical sword known as Lethal Bringer, a gift from Liselotte. This enchanted blade enhances her physical strength and slicing power, and any wounds it inflicts are cursed to heal slowly, making it a terrifying weapon in close-quarters combat. Her abilities have earned high praise from the protagonist, Rio, who has stated that her close-combat skills are superior to those of Sara and nearly on par with the renowned knight Alfred Emerle. During an ambush, while the knights accompanying her were preoccupied with protecting her as a weak woman, Aria single-handedly defended an entire flank against a horde of goblins, orcs, revenants, and even killed a minotaur, leaving the knights thoroughly ashamed.

Beyond her relationship with Liselotte, Aria maintains a close friendship with her former academy classmate, Celia Claire. She was deeply worried when she learned of Celia's kidnapping during her wedding and was greatly relieved to discover she was safe and under Rio's protection. Their friendship is depicted as one of mutual care and support, with the two women even sharing private complaints about the difficulty of finding suitable romantic partners. Aria also has a professional relationship with the other maids in Liselotte's service, including Cosette, Natalie, and Chloe, over whom she is the hierarchical superior. Her relationship with Rio develops further over the course of the story. She accompanies him on a mission to rescue Liselotte after she is kidnapped by Erika, showcasing her bravery and determination. Later, Rio trusts her enough to share many of his secrets, including the existence of the rock house and spirit arts, a trust she reciprocates by explaining the powers of her enchanted sword. Through her observations, she comes to understand his selfless nature and why so many women are drawn to him. Her skills have also garnered the attention of other powerful figures, such as Louise Sharon and Vanessa Emerle, who were deeply impressed by her mastery of Beltrum's swordsmanship style.