Ryo Miyaichi comes from a sporting family, with father Tatsuya being a former baseball player who played for and later managed the Toyota Motors baseball club, and brother Tsuyoshi also being a football player. Miyaichi started playing football in his elementary school years at Sylphid F.C. in Nagoya. He entered Chūkyōdai Chūkyō High School and played for the school football club. In the 2010 season, the team advanced to the All Japan High School Soccer Tournament but were defeated in the first round.