Mayuko Chigasaki is the central human protagonist of the story. She is a young woman in her late teens who has recently graduated from high school and is attending a cram school in preparation for college. Having no place of her own, she rents a small room at the Enohana Bathhouse, a countryside bathhouse that is struggling financially due to a lack of customers. Her living situation is precarious and she must work diligently to support herself.

Her character is defined by a strong sense of responsibility, diligence, and honesty. She is hardworking and polite, always striving to make ends meet with limited resources. Beneath this composed exterior, she is deeply self-conscious and introverted, often carrying a quiet melancholy. She lives away from her family and expresses a lot of emotional weight, feeling the pressures of her studies and daily survival. This insecurity makes her prone to self-doubt and easily overwhelmed by stress, yet she remains fundamentally good-natured and reliable.

Mayuko’s primary motivation is to improve her circumstances through education and steady work. She attends cram school with the goal of advancing to college, which she sees as a path out of poverty. Her daily life is a constant balancing act between studying, working part-time jobs, and managing the bathhouse’s decline. She rarely has time for leisure, and her energy is almost entirely spent on mere survival.

Her role in the story is that of an anchor and a foil to the alien NieA, who takes up residence in Mayuko’s closet without permission. While NieA is carefree, irresponsible, and seemingly unconcerned with consequences, Mayuko is the opposite—diligent, anxious, and burdened by practicality. The dynamic between the two drives much of the narrative, as Mayuko is forced to adapt to NieA’s freeloading and chaotic presence.

Mayuko’s key relationships include her close friend Chie Karita, who is described as being like a younger sister to her and a much more steady and supportive presence than NieA. She also interacts with other alien characters and townspeople, each of whom adds to her daily struggles and occasional moments of levity. Her relationship with NieA evolves from frustration to a grudging mutual acceptance, and through this unlikely companionship, Mayuko begins to open up slightly and find a sense of belonging.

Over the course of the series, Mayuko shows subtle development as she learns to cope with the unpredictable and alien elements in her life. She does not undergo a dramatic transformation, but her resilience and capacity for compassion grow as she navigates poverty, social alienation, and the absurdity of living with an alien. Her notable abilities are not supernatural; rather, they are her endurance, her organizational skills in managing a tight budget, and her unwavering commitment to her duties even when everything seems to be falling apart.