Bonobono is a young sea otter and the main character of his namesake series. His name was given to him by his father and is said to come from the sound a stone makes when it hits the sea. He lives with his father in a home on a cliff by the ocean, and his mother passed away when he was very young, a fact that is revealed later in the story.

Bonobono has an innocent, gentle, and deeply curious personality. His movements are slow, and his manner of speaking is often vague and meandering. He is easily amused by simple things but also becomes flustered easily, which is often indicated by the appearance of sweat droplets on his head. His defining trait is his endless curiosity about the world, and the story frequently follows him as he explores the mundane or unusual occurrences around him, asking philosophical questions about life, nature, and everyday mysteries. While he was originally portrayed as almost never getting angry, his character evolved over time to become more expressive, sometimes shouting or acting as a straight man to his friends antics. Despite his gentle nature, he is prone to wild, worrisome imaginations, frequently envisioning a terrifying figure called the Cave Man or Putaway Man who will seal him away for his misdeeds.

His primary motivation is simply to understand the world around him and spend time with his friends and father. He is not driven by grand ambitions but by a simple desire to play, explore, and find pleasure in daily life. His role in the story is that of the central observer and questioner. The narrative typically follows Bonobono as he becomes curious about a particular topic, leading him and his friends on a journey of discovery that is both comedic and oddly philosophical.

Bonobono has several key relationships. He lives with his father, a fellow sea otter who shares his son slow and seemingly dim-witted demeanor, though it is later implied that he is a legendary figure respected by even the largest sea creatures. Bonobono loves his father dearly and looks up to him. His best friends are a raccoon named Araiguma and a chipmunk named Shimarisu. Araiguma is short-tempered and often bullies the other two, frequently hitting Bonobono and Shimarisu for their foolishness, but he is a loyal friend. Shimarisu is timid and skittish, always asking others if they are going to bully him, and carries a walnut at all times. The trio forms a classic comedic dynamic. Bonobono also respects the Fishing Cat, a powerful and wise outsider who often provides thoughtful answers to his many questions.

In terms of development, Bonobono has undergone changes from his earliest appearances. His character design has become slimmer over the decades, and his personality has shifted from being completely passive to being capable of outbursts and comebacks. A significant piece of his backstory revealed later is the death of his mother, Raco, shortly after his birth, adding a layer of melancholy to his otherwise carefree life.

Bonobono possesses several notable abilities. As a sea otter, he is an excellent swimmer and diver, though he is slow and clumsy on land. He is almost never seen without a clamshell, which he carries for emergency food, reflecting the real-life habits of sea otters. He can use the shell to make tapping sounds. Despite his usual slowness, he has demonstrated surprising hidden strength on rare occasions, such as when he ate a poisonous mushroom and became violent, or when he single-handedly held onto a rope to prevent a fall. However, his most defining ability is his unique, meandering way of thinking, which leads him to ask simple yet profound questions that are the heart of the series.