Masami was first brought into RC car racing at the age of seven by his father Masaaki; a former motorcycle racer,[3] who finished 2nd at the 1971 Suzuka 6 Hours,[4] a research and development employee of ABC Hobby and later with Yokomo and radio controlled car racer and designer, when he brought him a Tamiya Lamborghini Countach.
[2] In 1987, during a world championship round for the 4WD off-road at Romsey, England, Hirosaka arrived as a privateer with a Schumacher CAT, bar being provided power sources from HPI Japan.
He had shown promise during practice and was brought into attention by Phil Booth, Schumacher's works driver[5] who referred him to Cecil Schumacher, who provided him a longer wheelbase version called the CAT XL, then unavailable in Japan and was raced by a majority of racers.
[7] In a 1998 interview with Germany's KEIL DTM magazine, Hirosaka listed his other hobbies as computers and theater.
His father who is now semi-retired, runs an RC car preparation service whilst doing contract work for Kyosho.
In his later career, he mentored teammate and compatriot Naoto Matsukura[8] and was the lead organizer of the 2015 IFMAR 1:10 Electric Off-Road World Championship.