On July 17, S.M. Entertainment announced that f(x) would return to the Korean music market with their second full-length studio album Pink Tape on July 28, 2013 after a year of absence. On the same day, the agency also uploaded a teaser picture of Krystal onto f(x)'s official website. On July 18, S.M. uploaded teaser pictures of Victoria and Amber. Four days later on July 22, S.M. Entertainment uploaded the music video teaser to the album's title track, "첫 사랑니 (Rum Pum Pum Pum)", onto their official YouTube channel.
With less than half the week to rack up sales and downloads to chart on the K-Pop Hot 100, the song still was able to debut in the top 20, landing at number fourteen for the week of August 10, 2013. A week later, the song topped the chart, marking the group's first number one single on the Korean Billboard charts.