Miyakawa made her international debut at the 2013 International Gymix where Japan won the bronze medal in the Junior Cup. At the 2013 Japan Junior International, Miyakawa finished twelfth all-around, fifth on vault, and won a bronze on floor. Miyakawa began the 2014 season at the City of Jesolo Trophy. The Japanese junior team finished in fourth, and Miyakawa finished seventh all-around with a 53.200. She also finished seventh in the vault and beam event finals. At the Junior Asian Championships, the Japanese team won gold, and Miyakawa won bronze all-around with a 53.650. She also won gold on vault and floor. Miyakawa was selected to compete for Japan at the 2014 Summer Youth Olympics. She finished fifth in the all-around final with a 53.300. She won a bronze medal in the vault final behind Wang Yan of China and Ellie Downie of Great Britain. Downie and Miyakawa had tied for second place with 14.566. For the tiebreaker, the highest scoring vault for each gymnast was used to determine who won the silver and who won the bronze. Downie's highest vault score was 14.866, and Miyakawa's was 14.800. Miyakawa ended her junior career at the Élite Gym Massilia where she finished seventh with her team and twenty-eighth all-around.
Senior career
Miyakawa's senior international debut was the 2015 WOGA Classic. She finished for sixth in the all-around with a 54.350, and she won a silver on vault, finished fourth on bars and seventh on floor. She finished seventh all-around at the Japanese National Championships, and she finished sixth all-around at the NHK Cup. At the Japanese Individual Event Championships, Miyakawa won gold on vault with a 14.925 average and finished fifth on floor. She was then named to the Japanese team for the 2015 World Championships along with Natsumi Sasada, Aiko Sugihara, Asuka Teramoto, Yuki Uchiyama, and Sakura Yumoto. At the 2015 Asian Championships, Miyakawa and the Japanese team won gold by almost a point over China. Miyakawa won a silver on vault behind Wang Yan with a 14.812 average, and she won a bronze on floor with a 13.600. At the 2015 World Championships, the Japanese team finished in fifth. In the floor final, Miyakawa scored a 14.933 and tied for fourth with Shang Chunsong.
