ロシアンルーレット
After releasing "Doggedly" as a prologue single, on January 31, 2012, B2M Entertainment officially announced that the group would have their formal debut with a mini-album, titled "Russian Roulette". On February 2, a teaser video of the music video of "Russian Roulette" was released on B2M Entertainment's YouTube account. On the following days, more photos of the music video and concept of the mini album were released. The teaser caught the attention of the public due to the girls playing Russian roulette on a table. The music video was released one week after, on February 8, same day of mini-album's release. On the same day, B2M entertainment revealed more details of the members. After promoting "Russian Roulette", B2M Entertainment announced the re-release of the mini-album under the title "Painkiller", with the song of the same name being the promotional song. The agency revealed some photos of the concept on March 26.