Sui Shijima, Ohana Matsumae's maternal grandmother, owns and operates the traditional Kissuiso hot spring inn at age 68. She possesses grey hair and brown eyes. Sui adheres strictly to traditional management, emphasizing quality service and the principle that "the guest is king," rejecting modern competitive tactics employed by rivals like Fukuya Inn. Her initial demeanor is strict and uncompromising. When Ohana arrives at Kissuiso, Sui treats her solely as a regular employee, demanding formality such as the address "Okami-sama" (proprietress) and granting no special privileges. This strictness extends to all staff; she disciplines significant errors physically while expecting unwavering dedication and professionalism. This sternness partly originates from her fractured relationship with her daughter, Satsuki, whom she disowned after Satsuki's rebellious departure from Kissuiso years earlier. This estrangement causes Sui to initially project resentment toward Ohana, viewing her as an extension of Satsuki's faults.

Beneath her rigid exterior, Sui demonstrates deep care for Kissuiso's legacy and her staff's well-being. Her backstory reveals she prioritized work over family, particularly during her husband's final days, a regret that surfaces during reflection. This vulnerability emerges amid Kissuiso's financial struggles and eventual closure, where she acknowledges her employees' loyalty and expresses gratitude for their efforts. Her character development includes reconciling aspects of her past, recognizing similarities between her own dedication to work and Satsuki's similar drive, and gradually softening her leadership approach.

In *Home Sweet Home*, Sui's background is further explored through logbooks discovered by Ohana, detailing Satsuki's time at Kissuiso. Flashbacks depict a younger Sui clashing with Satsuki over her daughter's desire to leave for Tokyo. Despite their conflicts, Sui ultimately approves of Satsuki's departure after recognizing her daughter's resolve, mirroring her own determination. The film also shows Satsuki visiting Kissuiso with infant Ohana, where Sui reaffirms her commitment to not be outdone in dedication.

Her relationships are defined by duty and latent affection. She guides Ohana indirectly through challenges, such as advising Nako Oshimizu to "be yourself," which influences Ohana's growth. She relies on her son, Enishi, though their dynamic is marked by her high expectations. Her eventual acceptance of Enishi's marriage to consultant Takako signifies a subtle shift toward familial reconciliation.