Number Nine was released by South Korean girl group T-ARA in 2013 as the lead single from their mini-album Again, and it became one of the group's best-known dance tracks of that era. Its strong choreography and instantly repeatable chorus helped it travel beyond Korean music shows into fan-made dance covers, reaction videos and compilation edits online. Years later, the short chorus hook still works well as a standalone sound because it is immediately recognisable to K-pop fans, even without the full song, and it evokes the polished dance-pop style that defined T-ARA's comeback period.