In 1999, at the age of 16, he won the first Nintendo-sponsored Smash tournament at Smash Bros. Fighting Battle: Smash Bros. Meijin Deciding Game, then played at Spring Selection Tournament Championship and the Super Mario Club National Tournament, which were officially broadcast on the Japan-only TV show 64 Mario Stadium in 2000. He later played at Japan United Smash Festa Round-Robin 1. His high placements made him one of the best early Smash 64 players in Japan. He then played in Premium Fight, the first Melee tournament.
Since 2014, he has provided live commentary for official Nintendo events such as Next Generation World Hobby Fair 2015, 2-on-2 WORLD GRAND PRIX JPN vs USA, and Smash Bros. Ultimate Spring Brawl Festival. In 2017, he joined esports organization Team GRAPHT.
Oikawa continues to enjoy the Smash Bros. series casually and has no plans to compete in tournaments again.