Well, they're not Japanese and they don't even play 'pop' music, but the The Japanese Popstars are one of the most popular electronica/house DJ groups going these days. Check out this very cool video for their "Facemelter" single released earlier this year:
The Japanese Popstars are Decky Hedrock, Gary Curran, and Gareth Donoghue. This group will appear at the upcoming Fuji Rock Festival. You can find out more information and download about five hours of their music tracks for free at The Japanese Popstars Podcast