Koyo Aoba is a member of the Simon Famiglia. He previously attended Simon Middle School, but he and his family transferred to Namimori after an earthquake hit their area. They chose Namimori because it is relatively earthquake free and they are invited to the Vongola Decimo's Inheritance Ceremony. Koyo uses boxing gloves as his weapon, just like Ryohei. Both he and Ryohei also have the same temper, as seen when they quickly get angry and neither of them want to stop the fight. He is sensitive over his contradictory name (Aoba meaning "green leaves," and Koyo meaning "red leaves"). He is firm in his belief that, no matter what his first and last name mean, they are still the same leaves.