That song is Mr.
The singer is Kara, a five-member girl group from DSP Company. The leader is Park Gyu Ri, and the members are Han Seung Yeon, Goo Hara, Nicole, and Kang Ji Young.
The strongest and most popular Korean girl groups in Japan right now are 2NE1 and Kara, followed by 4minute. Girls’ Generation just recently debuted in Japan, and the response is not as good as Kara.
The strongest and most prosperous Korean boy group in Japan is BigBang, followed by TVXQ, F.T.Island, Super Junior, and SHINee.
Japanese girl group AKB48 and Morning Musume are the strongest.
The boy groups are W-inds and SMARP15 are the strongest.