Azusa Aizawa is the central character of the story, a former Japanese office worker who died from overwork at the age of twenty-seven. After her death, a goddess granted her a new life in a fantasy world, where she requested only the ability to live an unhurried, peaceful existence. To ensure this, she asked for eternal youth and was reincarnated as an immortal witch, taking on the permanent physical appearance of a seventeen-year-old girl with long blonde hair and blue eyes.

She settled into a quiet home on a high plateau near the rural town of Flatta, where she became known locally as the Witch of the Highlands. For three centuries, she sustained herself by doing small amounts of work, such as gathering herbs to make medicine and hunting the low-level slimes that appeared near her home, selling the magic crystals they dropped for a modest income. She intentionally avoided any strenuous activity or grand adventures, dedicating herself instead to a slow, simple routine that was the complete opposite of her exhausting former life.

What Azusa did not realize was that a passive skill was doubling all the experience points she earned. After three hundred years of killing approximately twenty-five slimes a day, this gradual accumulation had pushed her to the maximum possible level of ninety-nine, making her the most powerful being in the world. The discovery of her immense power shattered the solitude she had carefully maintained, as news of her strength began to attract challengers, curious visitors, and people in need of her aid.

In terms of personality, Azusa is defined by her deep-seated desire for peace and her fierce opposition to overwork. Having died from exhaustion in her previous life, she is highly sensitive to anyone pushing themselves too hard and often steps in to enforce rest and balance on those around her. She is fundamentally a kind and hospitable person who cannot ignore someone in trouble, despite her general wish to avoid getting involved in other people's affairs. This inherent compassion frequently draws her into new situations and expands her household. She values harmony above conflict and prefers to resolve problems through words or creative solutions rather than violence, though she will use her power decisively when her peaceful life or her family is threatened. She has minor insecurities about her physical appearance, particularly her bust size, and her family has noted that her ability to come up with names is a notable weakness.

Her role in the story is that of a reluctant but powerful guardian and matriarch. Rather than seeking out adventures, she serves as a magnet for them, with various characters arriving at her home and becoming part of her life. Her primary motivation shifts from maintaining personal solitude to protecting the unconventional family that gradually forms around her. She takes on maternal and mentorship roles, guiding and caring for those who come to live with her, including her two adopted daughters who were born from the spirits of the slimes she killed.

Key relationships form the core of her new life. The red dragon Laika was her first challenger and, after a brief battle, became her devoted disciple and helper around the house. Two young girls, Falfa and Shalsha, manifested from slime spirits; Falfa immediately called Azusa her mother, and Shalsha initially sought revenge before being pacified and also joining the family as a daughter. She later welcomed Halkara, a clumsy elf fleeing a misunderstanding, and Rosalie, a ghost who was haunting a factory site. She also formed a strong alliance with Beelzebub, a high-ranking demon who became a close friend and frequent visitor. Through these connections, Azusa, who had died alone and exhausted in her first life, found herself surrounded by a loving and chaotic chosen family.

Over the course of the story, Azusa undergoes a subtle but significant development. She begins as someone who wanted to avoid deep connections, believing that as an immortal, she would only experience the pain of outliving others. However, as she bonds with her family and friends, she embraces her role as a protector and mother figure, finding fulfillment in relationships she never expected to have. Her character arc is about learning that a peaceful life does not have to be an isolated one, and that using her power to care for others is a meaningful way to spend her eternity.

In terms of abilities, Azusa possesses maxed-out statistics, granting her immense magical power, speed, intelligence, and physical strength far beyond normal limits. She has a unique ability called Magic Creation, which allows her to invent new spells, though this requires significant time and theoretical study. She can use a wide range of magic, including elemental manipulation of fire, wind, earth, ice, and lightning, as well as teleportation, flight, barrier creation, magical reflection, healing, mind control, invisibility, and summoning. Despite this arsenal, she rarely uses powerful attack magic, partly because she does not know how to control the force and fears causing unintended destruction. She also possesses superhuman physical strength, which she can use in close combat even without formal martial arts training.

Despite her overwhelming power, Azusa has several notable limitations. She has no special resistance to status ailments caused by poison, mushrooms, or curses. She is also afraid of ghosts and cannot see them unless they choose to manifest physically, a weakness that complicates her relationship with the ghost Rosalie. Her preference for a quiet life means she often hides her true strength, using fake names and avoiding displays of power when among humans or other powerful races unless absolutely necessary.