Oikawa is the setter and third-year captain of the Aoba Johsai High School volleyball club. He was also Kageyama's senior when they both attended Kitagawa Daiichi Middle School. According to Kageyama, he is a talented volleyball player with a bad personality. He is called "The Great King" by Hinata. He is essentially the child of the team, the rest of his club frequently being exasperated by his antics, flirting, and alien trivia. It is revealed that in his past, Oikawa was jealous of Kageyama's genius-like qualities, and still is, thus vowing to beat him in Aoba Johsai.