Kenichi Ōno is a male third-grade student who appears as a supporting character. He is referred to by Maruko as Ōno-kun. Physically, he possesses short black hair with bangs that are similar in style to Maruko's, while the rest of his hair consists of many locks jetting downwards to the left side, with less kept on the right. He also has gradually thickening straight eyebrows, a trait he shares with his best friend, Sugiyama. His typical attire includes a blue long-sleeve shirt with a white collar and a matching pocket on the upper-right portion, dark blue shorts, white socks, and dark orange shoes.

In terms of personality, Ōno is serious to an extent but is also understanding and carries a large sense of justice when dealing with class problems. He acts as one of the class leaders alongside Sugiyama, a role in which he can sometimes become pushy and strict to ensure others understand his orders. Despite his high social standing and physical strength within the class, he is willing and determined to help those who are weaker than him or who ask for his assistance. These traits earn him the favor of many girls in the class, yet he appears emotionally distant from them and speaks to both boys and girls with equal levels of consideration. He uses physical force in some situations where he sees other characters, often boys, bullying or misbehaving excessively, but only as a means to quickly stop them from potentially endangering others.

Ōno thoroughly enjoys playing soccer and discussing any topics related to the sport, as well as sports in general. His massive interest in soccer has made him thoroughly skilled in the sport, and he likewise enjoys teaching proper sports techniques to others in need of his help. His motivations are largely driven by his sense of justice and his role as a class leader, aiming to maintain order and assist his peers. Regarding his role in the story, he is a classmate of Maruko, and his key relationships include his mother and father as well as his classmates Sugiyama, Hanawa, Maruo, and Fuyuta. His most prized possession is a model ship he and Sugiyama built together, and his favorite foods include ramen and meat buns. There is no information available regarding any significant character development over the course of the series.