Girls' Generation had the highest revenue in Japan for 2012 out of all the Korean artists.
Oricon recently reported their annual revenue of artists in Japan. For 2012, they compiled the data from December 26, 2011 to December 17, 2012.
On the list of 'Total Revenue for 2012', Girls' Generation ranked 7th overall in all of Japan and ranked #1 for Korean artists. This year, the group released three singles, a full album, and videos on DVD and Blu-ray. Their total sales revenue came out to be 4,332,000,000 JPY (approximately $51.4 million USD).
KARA ranked 9th overall in Japan and was 2nd for Korean artists with 3,416,000,000 JPY (approximately $40.5 million USD). TVXQ ranked 17th overall in Japan and was 3rd for Korean artists with 2,041,000,000 JPY (approximately $24.2 million USD).