A former average competitor in the MFJ All Japan Road Race GP250 Championship between 1999 and 2004 (25th in 1999, 11th in 2000, 20th in 2001, 5th in 2002, 8th in 2003, 5th in 2004), Nakasuga moved into the All Japan Superbike Championship with the SP Tadao Racing Team in 2005, still with average results initially (12th in 2005, 9th in 2006), before joining the YSP Yamaha factory team in 2007 and finishing 4th.

Nakasuga had his premier class Grand Prix start at the Valencia circuit at the final race of the 2011 season as a replacement for the injured Jorge Lorenzo, finishing a creditable sixth place.

In 2012, he made a wild-card appearance for Yamaha at his home race at Motegi, finishing ninth, before making another appearance for the factory team at Valencia, this time in place of the injured Ben Spies.

Taking advantage of a wet circuit and numerous retirements ahead of him, Nakasuga was able to finish a distant second behind race winner Dani Pedrosa, becoming the only Japanese rider to score a podium finish in any class during 2012.

He won the Suzuka 8 Hours a record setting four times in a row, in 2015 with Pol Espargaró and Bradley Smith, in 2016 with Espargaró and Alex Lowes and in 2017 and 2018 with Lowes and Michael van der Mark.