Oiso's career began in the 2002–03 season at Pro Tour Boston as part of Hato Beeam with teammates Takao Higaki and Kazuki Ueno.
He made it all the way to final, beating José Barbero and Tsuyoshi Ikeda, before losing to Mattias Jorstedt.
This finals appearance, along with a pair of Grand Prix top eights, was enough to earn him the title of Rookie of the Year.
The following season, Oiso proved that the year before was no fluke with Pro Tour top eights in New Orleans[8] and San Diego.
Despite skipping Pro Tour Philadelphia,[11] he was a strong contender for Player of the Year, finishing just three points behind Olivier Ruel, and four behind Kenji Tsumura who won the title.