Music career
Hirano's music career began as part of the band SpringS, which was active from 2002 to 2003. She then released two character image songs in 2005: "Kimi Kara Onegai My Saint" (キミからお願い★my saint), which was used as an ending theme to the original video animation Itsudatte My Santa!, and "Futari no Imi" (二人の意味), which was an image song for her character Mamori Anezaki in the anime series Eyeshield 21.
Hirano's first solo single under the record label Lantis was "Breakthrough", which was released on March 8, 2006; the title track was used as the opening theme of the visual novel Finalist. Her next single was "Bōken Desho Desho?" (冒険でしょでしょ?, It's an Adventure, Right Right?), which was released on April 26, 2006; the title track is used as the opening theme of The Melancholy of Haruhi Suzumiya. The CD sold out in Japan the very day it was released. This was followed by the release of an image song single for her character Haruhi Suzumiya on July 5, 2006, which contained the songs "Parallel Days" (パラレル Days) and "SOS nara Daijōbu" (SOS ならだいじょーぶ). Her third single "Ashita no Prism" (明日のプリズム) was released on September 6, 2006.
Hirano released her fourth single "Love Gun" on October 10, 2007. This was followed by her fifth single "Neophilia" which was released on November 7, 2007, and her sixth single "MonStAR" which was released on December 5, 2007.
Hirano released her seventh single "Unnamed World" on April 23, 2008; the title track was used as the ending theme to the anime series Nijū Mensō no Musume. This was followed by the release of her first solo album Riot Girl on July 16, 2008. She then released the song "Namida" (涙 NAMIDA ナミダ) on October 8, 2008, which was used as the ending theme to the anime series Hyakko.
Hirano released her eighth single "Set me free / Sing a song!" on April 29, 2009. She then released her ninth single "Super Driver" on July 22, 2009; the title track is used as the opening theme of the second season of The Melancholy of Haruhi Suzumiya. Her second album Speed Star (スピード☆スター) was released on November 18, 2009. Her tenth single "Hysteric Barbie" was released on June 23, 2010. To promote the single, she created a Twitter account which was originally intended to be only used for one day; however, she would continue to use the account after the promotion had ended.
In May 2011, Hirano released a compilation album titled Aya Museum. Later that month, she announced via Twitter that she was no longer performing music for Lantis and had discontinued her music career until further notice. On August 2, 2011, Japanese magazine Bubka confirmed that she was dismissed by Lantis due to her sleeping with several band members. She then returned to music in 2012 and was signed to the record label Universal Sigma. Her first release on the label was the mini album Fragments on May 23, 2012. This was followed by the song "Zutto Kitto" (ずっと きっと) which was released on August 15, 2012; the title track is used as the ending theme to the anime film Fairy Tail the Movie: Phoenix Priestess.
In 2013, Hirano released two singles: "TOxxxIC" which was released on February 20, and "Promise" which was released on October 9; "Promise" was used as an insert song in the documentary film Kitakitsune Monogatari: Ashita e. She released her fourth album Vivid on February 19, 2014.
In 2018, Hirano performed the song "Pride", which was used as a character song to the mobile game Granblue Fantasy.
On April 24, 2020, Hirano posted a video of herself dancing and teaching the choreography of "Hare Hare Yukai" on her social media accounts to motivate others during the height of the COVID-19 pandemic, sparking the hashtag "#HareHareYukaiAtHomeWithAllYourMight" (#お家で全力ハレ晴レユカイ). This created a trend of cover dances of "Hare Hare Yukai" posted to the hashtag, participants of which included Tomokazu Sugita (the voice actor of Kyon) and Minoru Shiraishi (the voice actor of Taniguchi). This led "Hare Hare Yukai" to chart at no. 6 on the Billboard Japan Hot Animation in the same week.
On May 10, 2025, she released "Evolutions", a single under the Lantis label.