Nontan is a mischievous male kitten defined by his playful nature and curiosity. He explores his world, learning through interaction and discovery. His imperfections and occasional failures create relatability, making him an accessible figure for young audiences despite early discussions about his suitability as a role model due to his mischief.

Originally conceived as a fox, the character was redesigned as a cat. His name originates from his creator's daughter. Nontan resides in a house marked by a distinctive flag on its roof. Initially living alone, his home life changed when his younger sister Tartan joined him.

Nontan's age varies across stories, explicitly stated as four years old in one birthday-themed installment. His core personality of curiosity and playfulness remains consistent throughout all media, with no significant long-term evolution documented. He interacts with recurring animal friends: Buta-san, a piglet fond of apples; three six-year-old rabbit siblings; a tone-deaf three-year-old tanuki; and Kuma-san, an eight-year-old bear who acts as a leader. Tartan shares Nontan's mischievous streak and an affinity for mythical creatures like oni.

A silent bee character, Hachi-san, observes Nontan's activities, communicating nonverbally. Medical care is provided by Dr. Bear, a bear character treating Nontan during illnesses or injuries. His background and developmental arc consistently emphasize everyday adventures and learning experiences across book series and adaptations.