Junichirou "Jun" Kubota and Tomo Aizawa are the closest brothers you'll ever see. Although they fight and bicker, they always have each other's backs. However, there is one one issue—Tomo is in love with Jun! Since she was a little girl, tomboyish Tomo has been just another one of the boys. Because of his extraordinary muscularity, Jun has never been aware of any of her advances, not even when she admits it out loud. To make matters worse, he had no idea she was a girl for a very long time. Onnanoko Tomo-chan! the humorous antics of Tomo and her friends as they try to get Jun's attention and get out of the notorious brozone.