Kuro’s owner, often referred to simply as Grandpa or Jiisan, is one half of the elderly Fuji couple who live in the town of Sakuragaoka. He and his wife are a kindly, gentle-natured pair with no other known relatives, having found Kuro when the cat was a stray and taking him into their home without question. Since that day, they have treated the cat as a true member of their family, a warmth that the cyborg Kuro reciprocates in his own gruff way by fiercely protecting both them and their home from any and all threats.

In terms of personality, Grandpa is defined by an unwavering optimism and a pronounced lack of awareness regarding the bizarre situations that constantly surround him. He and his wife are portrayed as being exceptionally dense, often failing to recognize when they are in genuine danger, and possess a natural, almost supernatural, air-headedness. This oblivious nature is a core part of his character; he remains completely unaware that his pet cat is actually a powerful cyborg, as Kuro goes to great lengths to hide his metal body and secret identity.

Grandpa’s motivations are simple, rooted in a quiet, domestic life with his wife and their pet. The couple loves to travel together, but a shared, extraordinary lack of a sense of direction means they are perpetually getting lost and ending up in locations far from their intended destination. This tendency, combined with their general obliviousness, means they frequently wander into exactly the kind of trouble that Kuro must then resolve. Despite their constant need for rescue, they always approach everyone, whether friend or foe of Kuro, with unshakable kindness.

Within the story, Grandpa and Grandma serve as Kuro’s emotional anchor and his primary motivation for many of his battles. They are the embodiment of the peaceful, ordinary life he wishes to protect. Their vulnerability is a recurring plot device; villains, aware of Kuro’s attachment to them, will frequently kidnap the elderly couple to use as bait against the cyborg cat. The central relationship is, of course, with Kuro. While Grandpa showers the cat with affection, Kuro often expresses exasperation at the couple’s foolishness, yet he will go to any length to ensure their safety, demonstrating a deep, unspoken gratitude for the home they gave him. He has also been known to disguise himself as Kuro when the real cat is away, just to keep the old couple from worrying.

While the character does not undergo a significant personal journey or development, his consistent traits create the primary source of comic relief and emotional stakes in the series. His static nature is the point; he and his wife are a constant, unchanged, and innocent presence that grounds the chaotic world of cyborg cats and mad scientists. Regarding notable abilities, Grandpa possesses no special powers. Instead, his most defining traits are his extraordinary kindness, his remarkable ability to forget things and lose his way, and perhaps his most impressive skill: an almost impenetrable density that prevents him from ever discovering the incredible truth about his pet cat.