Aya made her acting debut in 1999 with Tengoku no Kiss, a Nippon Television drama, at the age of 15. From here on she established herself as a television regular with appearances in many Japanese TV dramas. In 2001, Hirayama played significant parts in the television drama Fighting Girl and the film Waterboys. Hirayama's most notable acting role to date is her leading appearance as Yoko in the 2004 South Korean movie Fighter in the Wind. In 2005, Hirayama played the title character Haruka in the Japanese television drama Haruka 17.