Aletta is a young demon, approximately twenty years old, originating from the Demon Kingdom on the Eastern Continent of another world. She possesses distinctive goat-like horns, a remnant blessing from the defeated Demon God vanquished by the Four Heroes roughly seventy years before her birth. This event drastically weakened her kind's demonic powers, leaving her physically nearly identical to humans save for the horns.

Seeking employment, she left the demon lands. Initial success turned to rejection and homelessness when her horns were discovered, forcing her to reside in a ruined dwelling and survive on sporadic one-day jobs. One night, she found a mysterious door leading to the Western Restaurant Nekoya. Inside, she consumed an entire pot of corn soup and fell asleep, discovered by the Master the next morning. Hearing her plight, he offered her a meal and employment as a waitress, initially one day per week (the "Day of Satur") for ten silver coins. This wage later increased to twelve silver coins after a year, and the position expanded into a permanent daily role.

Physically, Aletta has golden blonde hair typically styled in twin pigtails, bright green eyes, a petite build, and short stature. Her shoe size is 24 cm. Her Nekoya uniform consists of a white blouse with puffed sleeves and a frilled collar secured by a black ribbon, layered under a black frock with a full skirt ending above the knees. She wears a white apron with frilled edges tied at her waist, complemented by white ankle socks and black Mary Jane shoes. Her horns appear less prominent in manga illustrations compared to the anime, and her casual attire is depicted as more patched and worn in the manga. Earth garments provided by the Master, including notably soft undergarments, form part of her adaptation.

Personality-wise, she defies common demon stereotypes through her gentle, kind, and diligent nature. Early prejudice due to her lineage caused deep insecurity, but working at Nekoya fostered significant growth in confidence and social skills, aided by the Master’s consistent professionalism and Kuro’s companionship. Her courteous and energetic nature proved well-suited to service roles.

Professionally, she gained a second permanent position as a housekeeper, guard, cleaner, and maid for the regular patron Sarah Gold. This role provided stable housing and further bolstered her self-worth. Demonstrating initiative, she learned to prepare buttered potatoes (enhanced with bacon, cheese, and pepper) from the Master to improve Sarah’s diet during treasure-hunting endeavors. Sarah’s appreciative hug strengthened their bond, and Aletta fiercely interrupted a marriage proposal to Heinrich Seeleman by claiming Sarah as "hers".

Key traits include illiteracy in the Eastern Continent’s language, compensated by exceptional auditory memory allowing her to memorize Nekoya’s entire menu. She exhibits naivety regarding Earth technology, misinterpreting plumbing as magic, elevators as enchanted doors, and cardboard boxes as unfamiliar objects. Her culinary preferences evolved from steamed potatoes in Season 1 to corn soup/potage in Season 2, aligning with her first meal at Nekoya. Unlike other patrons, she lacks a fixed favorite dish and appreciates the staff meals prepared by the Master.

Significant relationships include protective dynamics; the Red Queen declared her part of her "treasure" under a "Declaration of Protection" upon her hiring at Nekoya.