Mon-san is a female cat and the eldest of the cats living with Kuru-san, the owner at the center of Kuruneko. She is a Scottish Fold mix with a black and white coat and odd eyes, one gold and one blue. As the first cat adopted by Kuru-san, she holds a special place in the household and is often considered the leader of the group, sometimes referred to as a delinquent or the first member of the cat gang. Her personality is independent and spirited, with a tendency to be assertive or bossy toward the other cats, though she also shows affection in her own way, especially toward Kuru-san. Mon-san's motivations are typical of a cat: she seeks comfort, food, attention on her own terms, and enjoys asserting her place as the alpha of the feline household. In the story, she serves as a central figure among the cats, often interacting with the other pets and reacting to Kuru-san's daily routines. Her key relationships include the other resident cats, with whom she has a mix of camaraderie and rivalry, and Kuru-san, whom she both relies on and tolerates with a regal air. Over the course of the series, Mon-san's character does not undergo dramatic change but is consistently depicted as a strong-willed, memorable feline with a clear personality. Her notable traits are her striking odd-eyed appearance and her dominant, no-nonsense attitude, which distinguish her from the more mild-mannered cats in the household.