In 2011, Hirai competed at the 2011 FINA World Junior Swimming Championships. He won a gold medal in the 200 meter butterfly and a silver in the 4x100 meter medley relay and the 4x100 meter butterfly.
In 2012, Hirai competed at the 2012 FINA Swimming World Cup. He finished 4th in the 200 meter butterfly.
Hirai also competed in the 2012 FINA Short Course Swimming World Championships. He competed in the 200 meter freestyle heats, finishing 30th. In the men's 100 meter butterfly heats, he finished 37th. He also competed in the 4x200 meter freestyle relay heat, finishing 5th, and the 50 meter butterfly heat, finishing 39th.
At the 2013 Summer Universiade, Hirai competed in the 4x100 meter freestyle and the 200 meter butterfly. He finished 5th in the 4x100 meter freestyle, and won the silver medal in the 200 meter butterfly.
Hirai later competed in the 2013 FINA Swimming World Cup. He swam in the 4x50 medley relay, finishing 5th. He also competed in the 100 meter butterfly, finishing 6th, and the 4x100 meter freestyle, finishing 7th.
In the 2014, Hirai competed at the 2014 Pan Pacific Championships in the 100 meter butterfly, finishing 7th.
Later, Hirai went on to compete in the 2014 Asian Games, and winning the silver medal in the 200 meter butterfly.
In October 2014, Hirai competed in the 2014 FINA Swimming World Cup. He swam in the 200 meter butterfly, finishing in 4th.
In 2016, Hirai competed in the 2016 FINA Swimming World Cup, placing 5th in the 200 meter butterfly.
Japan
