Aoyama was inspired to become a performer by
Janet Jackson. Her first release in the music world was a collaboration on DS455's single "Summer Paradise: Risin' To Tha Sun, feat. Aoyama Thelma". The single reached #46 on the
Oricon charts. On 9 September 2007, Aoyama made her solo debut with the single "One Way". This single debuted at No. 98 on the
Oricon charts. Two weeks later, Aoyama was featured on the hit single "Koko ni Iru yo" with fellow J-Soul artist SoulJa. The single stayed on the charts for many weeks. The single sold over 100,000 copies and reached No. 6 on the charts. In early 2008, Aoyama released an answer song to the single "Koko ni Iru yo" by SoulJa with her own single titled "Soba ni Iru ne" which also featured SoulJa. The songs are similar, and share the same chorus. However, the song "Soba ni Iru ne" proved to be more popular than the song "Koko ni Iru yo", debuting at No. 3 in its first week on the
Oricon charts, and in its second week reached No. 1 on the charts. "Soba ni Iru ne" stayed in the Top 5 ranking for 7 consecutive weeks. It became the highest-selling female single (strictly a duet song) on the Oricon 2008 yearly charts. The Japanese version of
Hachi: A Dog's Tale uses "Wasurenai yo" by her as its theme song. Her debut album,
Diary, was released in Japan on 26 March 2008. On 11 February 2009, she released the album
Love!: Thelma Love Song Collection, which debuted at the number-one position on the Oricon weekly charts. Her album
Emotions was released in September 2009. Aoyama collaborated with
Big Bang's Taeyang for her single, "Fall in Love", released on 27 January 2010. Aoyama's single "
Kaeru Basho" was released on 3 March 2010. The song was used in the movie ''
Doraemon: Nobita's Great Battle of the Mermaid King. This single features SoulJa, and has a B side called "Anata ga Kiechaisode". Summer Love!!'' featuring Red Rice came out in 2010. In 2010, she sang with the Taiwan pop group
Da Mouth in a duet with the female lead singer Aisa, on the song "Secret Life". The song appears on the album
Da First Episode. Aoyama collaborated with Korean girl group
4Minute on the single, "Without U", released on 25 May 2011. The English version was released on 7 May 2011. She contributed a cover of
hide's "
Tell Me" to the
Tribute VI -Female Spirits- tribute album, which was released on 18 December 2013. She played the character Megumi Natsui in the 2022 television series, "Riding a Unicorn." In 2021, Aoyama released her seventh studio album
Scorpion Moon. She later released in the following year with SoulJa. In 2023, Aoyama's label Universal J was dissolved following a restructure of
Universal Music Japan. She was transferred to
Polydor Records, however made no releases under the label. In 2024, Aoyama announced her departure from Universal Japan. Launching her own independent label, she revealed the title of her eighth studio album,
Easy Mode. The album was later released on 19 February 2025. == Personal life ==