Shiraiwa began skating in 2006, after being inspired by Shizuka Arakawa's 2006 Olympic victory. Mie Hamada became her coach when Shiraiwa was six years old.
She competed at the 2014–15 Japan Junior Championships but did not qualify for the free skate, having ranked 27th in the short program.
In November, Shiraiwa won the silver medal at the 2015-16 Japanese Junior Championships behind Wakaba Higuchi. A month later, at the JGP Final, Shiraiwa finished 5th. Making her debut at the Japan Championships on the senior level, she placed 5th, and was named as a member of the Youth Olympic and the Junior World teams.