They debuted in Japan in 2009 with an independently released mini-album, Now or Never. The album failed to chart, but the band picked up some fans who were already aware of frontman Jung Yong-Hwa through his acting role -- playing a boy band member, no less -- in the TV mini-series You’re Beautiful. After another mini-album, the band returned to Korea, where they were an instant smash hit, with their debut single "I'm a Loner" going straight into the charts at number two. Two hugely successful Korean mini-albums later, the band went back to Japan, where they then cracked the charts, presumably with the aid of fans who had followed their Korean successes, and landed a major-label deal with Warner Music. There is a big tradition of clever cross-marketing in East Asian pop, and this strategy really fueled the band's career, as it had for so many others; their success in one country fed their success in the other, and every time they went back and forth, they had a readymade stream of hits where all they had to do was re-record the vocals in the other language.
In their first few years they released more singles and full-length albums in Japan than in Korea, though at home they released a slew of mini-albums, a very popular format. Indeed, their eventual fame was greater in Japan, with their biggest success being the 2012 album Code Name Blue, which hit number one on the Oricon chart. Thanks to the Internet and the early-2010s international kitsch interest in K-pop, their fame spread throughout the world, and they played a number of overseas dates, notably at London's O2 in September 2012, a gig attended by more than 4,000 fans from all over Europe. In 2013 they became the first Korean rock band to undertake a world tour. ~ John D. Buchanan, Rovi