Ai Otsuka (Da Zhong  Ai , Otsuka Ai, born September 9, 1982) is a Japanese singer-songwriter from Suminoe-ku, Osaka, Japan. She is a popular artist on the Avex Trax label and is best known for her 2003 hit "Sakuranbo," which stayed in the Top 200 Oricon Weekly Singles Chart for 103 weeks. A piano player since age four, Otsuka composes and co-produces her own songs, as well as writes her own lyrics. Her music ranges from upbeat pop/rock music to ballads.

In April 2006, Otsuka released "Frienger" (a portmanteau of the words Friend and Ranger). The promotional video was shot in Taiwan and was used as the commercial song for the Toshiba W41T 4 GB MP3 mobile phone. Soon after the release of "Frienger," Otsuka reprised her role as an actress for Tokyo Friends: The Movie, which hit theaters in Japan on August 12, 2006. The movie is a direct sequel to the DVD drama released the previous year. Otsuka also sang the opening theme for Tokyo Friends, "Yumekui", which was released as a new single on August 2, 2006. It debuted fifth on the weekly chart, selling 63,428 copies in the first week and a total of 145,281 copies.  Two months after "Yumekui", Otsuka released another single titled "Renai Shashin" on October 25, 2006, which was used as the opening theme song for the movie Tada, Kimi o Aishiteru. The song was based on events from the film and its original novel, also called Renai Shashin. "Renai Shashin" debuted at number 2 and sold 129,855 copies, making it the 75th best-selling single of the year. At the end of 2006, Otsuka had released a total of three singles and charted on Oricon's 2006 yearly chart with "Frienger" at number 60, "Yumekui" at number 66, and "Renai Shashin" at number 75.  Otsuka released her fourteenth single, "Chu-Lip," on February 21, 2007. The single was used as the theme song for the TBS drama Kirakira Kenshui, starring Manami Konishi and Wentz Eiji of WaT and managed to claim the third position on the Oricon charts.

Answer the following question by taking a quote from the article: What was the last song she released?
Otsuka released her fourteenth single, "Chu-Lip," on February 21, 2007.