A former member and setter of Kitagawa Daiichi Junior High, he won the "Best Setter Award" in his prefecture during his 3rd year at the aforementioned school. As a former upperclassmen and senior setter to Tobio Kageyama, he nearly hit him once after Kageyama requested that he teach him to serve, but was held back by Hajime Iwaizumi. He later felt guilty and showed remorse, and apologized to Kageyama.He'd been blessed with more athletic skill than most people. A good sense for things, too. Even so, there was an ever-present wall he couldn't overcome. The junior high section of Shiratorizawa Academy, which had become known as the strongest in the prefecture, and the "Herculean" Wakatoshi Ushijima, who numbered among its players.
In his final tournament of junior high, he and his team faced the Shiratorizawa team and won a set for the first time. They came in second to Shiratorizawa in the results, and it was there that Oikawa received the Best Setter Award.