The mother figure in Chi's Sweet Adventure is Miwa Yamada, the human mother of the young boy Yohei and the wife of Kento. Her background establishes her as a capable and nurturing woman who was once the senior of her husband during their university days, a small detail that hints at a confident and accomplished personal history. In the story, she is the one who, alongside Yohei, first discovers the lost kitten, Chi, and makes the compassionate decision to bring her home. Her personality is defined by a gentle, patient, and deeply caring nature. She is understanding and warm, handling the chaos of a growing kitten and the secret of keeping a pet in a no-pets housing complex with remarkable composure and creativity. Her primary motivation stems from a desire to provide a loving, stable, and happy home for her family, including the newly adopted Chi. She acts as the emotional anchor of the Yamada household, consistently prioritizing the well-being of both her son and the kitten.

Her role in the story is central yet supportive. She serves as the primary caretaker and disciplinarian for Chi, guiding the kitten through daily life, from mealtime to bath time, and teaching her about the world inside the apartment. She also manages the household's delicate situation with the landlady, often coming up with clever solutions to keep Chi hidden. In terms of key relationships, her bond with Chi is one of adoptive mother and kitten, filled with tenderness and gentle correction. Her relationship with Yohei is that of a loving and involved parent, and she shares a warm, cooperative partnership with her husband, Kento, as they navigate parenthood and pet ownership together. Her character undergoes subtle development as she becomes more attuned to Chi's needs and personality, growing more relaxed and adept at integrating the kitten into their lives. While she does not possess superhuman abilities, her notable skills include her resourcefulness, her keen observational sense for when Chi is in trouble, and her ability to maintain a calm and cheerful demeanor even in stressful situations, which keeps the family unit cohesive and loving.