Kojirō Kageyama is a student at Oosugi High School and the childhood friend of Eiichirō Maruo, having lived near him and attended the same schools since elementary school. They first became close during a fifth-grade sports festival, and Kageyama has long sensed that Maruo would achieve something significant. He is a member of the shogi club and is notably strong in mathematics, even outperforming the studious Maruo in that subject. He also has a younger sister. Kageyama is competitive and results-driven, approaching tennis with a strong emphasis on winning and practical outcomes. He is straightforward and uncompromising in his dealings with others, often prioritizing results over emotional considerations. This attitude embodies the harsh realities of competitive junior tennis and serves as a contrast to the more analytical and methodical approach of the protagonist. Despite his sharp edges, Kageyama is a loyal friend who frequently attends Maruo’s matches, offering both teasing and genuine support. He has a strategic side that extends beyond shogi, as he keenly observes those around him and occasionally maneuvers situations to his own advantage, such as when he helps arrange opportunities for Maruo while also pursuing his own interests. He is also aware of Himeko Sasaki’s feelings for Maruo and harbors his own romantic interest in her. As a tennis player, Kageyama displays an aggressive style with fast decision-making and a powerful build. His presence in the story emphasizes the competitive structure of the tennis world and the importance of results, pushing both himself and the protagonist to measure up. Through his interactions with Maruo, Natsu Takasaki, and coach Fukuzawa, Kageyama remains a grounded figure who highlights the tension between friendship and ambition within a rigorous sporting environment.