A photo of singer BoA and f(x)'s�Amber has been gaining a lot of attention lately. BoA tweeted yesterday, "During SMTOWN's Tokyo concert. With my little sister Amber". The two posed affectionately for the camera, with BoA leaning on Amber's shoulder.� Fans and followers commented, "Who's older and who's younger?", "You look amazing today as well," and "I want to see the concert too." BoA, f(x), and other artists from SM Entertainment will be performing in Tokyo from September 2nd to the 4th. Source + Photo: Osen via Nate