The rivalry between Oikawa and Kageyama in the anime "Haikyuu!" is significant as it showcases the contrasting styles and approaches to volleyball between the two characters. Oikawa is portrayed as a strategic and experienced setter with excellent social skills, while Kageyama is depicted as a talented but less socially adept setter with raw potential. Their rivalry pushes both characters to grow and improve, with Oikawa serving as a mentor figure to Kageyama despite their competitive dynamic. The rivalry also highlights themes of teamwork, leadership, and determination throughout the series.