Ojii-chan is an elderly woman who discovers the stray cat Tsushima scavenging through garbage cans. She takes him home to feed him properly. Even after learning Tsushima can speak, she adopts him and indulges his whims. Her name, meaning "grandfather" in Japanese, causes frequent confusion as she is female.

She adores cats, allowing them free access to her home. Multiple cats live with her, including the authoritative long-term resident Miss Zun, the timid and pampered Cha, and the wary neighborhood stray Osamu, who remains cautious despite her long-standing kindness. A past dream of owning a cat resembling a bear led her to initially mistake Tsushima for the "Tsushima cat" breed, though he looks little like it.

Her days center on caring for the cats, often leading to humorous or chaotic events. She harbors a strong dislike for insects, contrasting sharply with Tsushima's deep knowledge and fascination with them. A dream sequence reveals her enduring grief over a previous cat's loss, depicting her attempt to bring the deceased cat home only for it to walk away. The cats, especially Tsushima, offer her comfort during such moments.

Across official portrayals, she remains consistently nurturing and patient, tolerating the cats' diverse personalities and antics. Her home functions as a sanctuary for strays, reflecting her open-hearted care. The narrative emphasizes the quiet companionship and mutual dependence between her and the cats, with her daily routines and emotional well-being deeply connected to their presence.

Her background and development show no significant evolution beyond these established patterns of care and interaction. Her role provides stability and affection to the cats, while she subtly draws emotional support from their companionship.