The Japanese rider Watanabe started on pocket bikes when he was four and participated in several races in the Dijiro Cup, organized by the family and colleagues of former 250cc champion Daijiro Kato. From 2009 he participated in the J-GP3 category of the All Japan Road Race Championship and in 2012 moved to the Moto3 Championship of Spain as a steppingstone to the World Championship. It was in the fifth race at Albacete where he got his best result, finishing in third place. He contested the Japanese Grand Prix as a wildcard in 2011 and 2012, finishing in 16th place on his second attempt.