Yuzuko is Natsuo’s main rival throughout the story. Born in Japan, she moved with her parents to Brazil. While there she became an exceptional MMA fighter under the training of Mario Cordeiro. She is the captain of the budding MMA club at the Natsuo’s high school and is close friends with Mario Cordeiro daughter, Ringi. It is two early fights with Yuzuko that drive Natsuo to become an MMA fighter. Yuzuko has no talent, but makes up for this limitation with pure tenacity and a single-minded focus on moving forward. As a result, Yuzuko often comes off as "creepy" by others, who are disturbed by the level of enjoyment she derives from MMA.