Mineko Seki is the maternal grandmother of Oriko Seki, the protagonist of the story. She is an elderly woman in her seventies who has run the Harunoya Inn, a traditional Japanese ryokan in the hot spring town of Hananoyu, as the sole proprietress for many years. As the mother of Shoji Seki, she is the last remaining direct family member who can take in her granddaughter after Shoji and his wife Sakiko are killed in a car accident. It is this tragedy that brings Okko to live with her at the inn.

Mineko possesses a gentle, considerate, and mindful personality. She is deeply aware of the grief her granddaughter carries and is careful not to push her too hard or too soon. When she first considers asking Okko to help as a junior innkeeper, she hesitates because she does not know how to approach the subject given the recent loss of the girl's parents. This thoughtfulness defines her approach to both family and hospitality. She is a capable and experienced innkeeper who manages the inn on her own, embodying the traditional values of Japanese omotenashi, or wholehearted hospitality.

Her primary motivation is twofold. On a personal level, she wants to provide a stable, loving home for Okko and help her heal from the trauma of losing her parents. On a professional level, she is committed to preserving the Harunoya Inn and its legacy. She sees in Okko a potential successor and gradually, through guidance and example rather than force, encourages Okko to take on the responsibilities of a junior innkeeper.

In the story, Mineko serves as the anchor of Okko's new life. She is the reason Okko relocates to Hananoyu and the person who gently steers her toward the role of young innkeeper. While not always in the foreground of every episode, Mineko is the stable presence that allows the other characters to grow. Her experience and measured wisdom often provide the quiet support that Okko and the inn's staff rely upon.

The most significant relationship in Mineko's life is with her granddaughter Okko. Their bond deepens as Okko learns the trade and gradually finds renewed purpose and joy. Mineko is both a maternal figure and a mentor, offering patient guidance while allowing Okko to make mistakes and discover her own abilities. Another crucial relationship is with Makoto Tateuri, nicknamed Uribo, who was her childhood friend and one-time next-door neighbor. Uribo died young and exists as a ghost who remains attached to Mineko and the inn. He watches over her from the spirit world, and his unspoken devotion to her is a key reason he stays and eventually helps Okko.

Mineko's character development is subtle but meaningful over the course of the story. She begins as a solitary, capable innkeeper who has been managing everything on her own. Through Okko's arrival and gradual involvement in the inn's operations, Mineko learns to delegate, trust, and let go. She also confronts her own past, including the pain of losing loved ones and the bittersweet nature of her connection with Uribo. Her journey is one of passing on her legacy, finding new purpose in nurturing the next generation, and reconciling with the supernatural elements that linger around her inn.

While Mineko does not possess any overt supernatural abilities, her notable abilities lie in her mastery of traditional innkeeping. She is highly skilled in managing the inn's day-to-day operations, training staff, coordinating meals, and handling difficult guests with poise and tact. She also possesses strong emotional intelligence and perceptiveness, allowing her to understand what others are feeling even when they do not speak openly. These qualities make her an effective leader and a respected figure in the community.