Throughout the series, the relationship between Kageyama and Oikawa evolves from a competitive and tense dynamic to a mutual respect and understanding. Initially, Kageyama views Oikawa as a rival and feels pressure to prove himself against him. However, as they interact more, Kageyama learns from Oikawa's experience and skills, leading to a more cooperative and supportive relationship between the two characters. Ultimately, they develop a bond based on their shared love for volleyball and a deep respect for each other's abilities.