Hazedon is the titular protagonist of the 1972 anime series. He is a young goby fish who lives in the sea and, despite not being a particularly cool-looking boy, embarks on a grand adventure. His primary motivation stems from a promise made to his dying mother: to travel the world and become the strongest fish alive. This goal, which was initially his mother's wish, becomes his own driving purpose throughout his journey.

To aid him on his quest, Hazedon carries a few precious mementos from his mother. These include her flute, a seashell locket that is said to open only when he has truly become the strongest fish in the world, and a plastic bucket that he places on his head. His character is comically personified, possessing the unique ability to walk upright on his tail fin much like a human, while still being able to swim like a normal fish when in the water.

Throughout his travels to tropical waters, Hazedon is not alone. He is joined by two close companions: Puyan, a blowfish, and Shiran, a mermaid. Together, the trio faces various challenges and adversaries. Notable antagonists include Samegirusu, a nasty shark, and Ankoragon, an anglerfish, who frequently try to chase and bully Hazedon. Despite these threats, he typically manages to escape with the help of his friends. His journey is one of growth and adventure, depicting his development as he strives to fulfill his late mother's wish.