In 1999 Harada moved up to the 500cc class to compete on Aprilia's 380cc V-twin race bike. He obtained top 5 finishes in the first 10 races, including podium results at Paul Ricard and Donington Park: however, the bike's performance subsequently faded and he could not improve his results. In 2000 he was less competitive, coming 16th overall.
In 1999, Harada transitioned to the 500cc class on Aprilia's 380cc V-twin race bike and achieved top five finishes in the first ten races, including podium finishes at Paul Ricard and Donington Park. However, the bike's performance deteriorated, hindering his results. In 2000, he experienced a decline in competitiveness, finishing 16th overall.