AKB48 are an all-female Japanese theater troupe/musical unit created by the famous producer Akimoto Yasushi. "AKB" is short for Akihabara, a Tokyo district where the group gives daily performances in its own theater, and 48 is supposed to point out the number of members in this populous teen squad, although it's more of an approximation. Yasushi established AKB48 in 2005 by holding an audition attended by 8,000 participants, who were filtered down to 20 girls; the winners debuted on-stage in 2005 as AKB48's Team A. In 2006, Yasushi teamed up with a telecom firm to produce the world's first ever audition based on mobile-phone-mailed submissions, which attracted close to 12,000 hopefuls, 18 of whom became Team K. The third unit -- naturally, Team B -- followed later the same year; the producers briefly toyed with the idea of reorganizing AKB48 into two bunches, Baragumi and Yurigumi, but ultimately dropped it. The band debuted with the single "Sakura No Hanabiratachi" (2006), which sold 46,000 copies -- a decent result for an indie label release -- and by the third single, "Aitakatta" (2006), they were picked up by DefSTAR Records, a sublabel of Sony Music. They then proceeded to confirm that there's nothing like a little scandal to make headway in showbiz: the single "Seifuku Ga Jama Wo Suru" (2007) rose to number seven -- the band's chart record -- propelled by rumors that it referenced a specific Japanese type of voluntary underage prostitution, an eyebrow-raising topic for a bunch of teen girls. AKB48 played it down, confirming that they were into social critique with their next single, "Keibetsu Shiteita Aijou" (2007), which dealt with bullying.
All in all, 2007 was a busy year for AKB48: they delivered a barrage of big releases, simultaneously cranking out six full-length albums (three by Team A and three by Team K) and a stack of seven stage DVDs (again, by those two teams only); besides, several girls starred in the movie Densen Uta, and the whole group starred in the mega-popular new year TV show Kohaku Uta Gassen. The third branch of AKB48 released its own DVD in 2008, when the group also compiled the Set List: Greatest Songs 2006-2007 CD, which sold 27,000 copies. Inevitably with a cast of this size, the lineup adjusted constantly, with several girls "graduating" in 2007-2008, and one, Kikuchi Ayaka, kicked out for the sin of getting caught on camera in the company of a boy. Unperturbed by personnel shifts, AKB48 continued to perform and record, releasing three singles in 2008 and following those in 2009 with Oogoe Diamond, which sold 65,000 copies, and Namida Surprise!, their first gold release (134,000 units sold). They confirmed their rising popularity by scheduling two gigs at the Budokan with their "sister band," SKE48, the same year.