Many people using Amazon for predict USA sales. And that's correct. But people should used amazon even for predict the japan weekly sales, usually amazon is 90% accurate even in this case.
That said.
http://www.amazon.co.jp/gp/bestsellers/videogames#1
#14 PS4 1TB
#24 WIU
#36 WIU MK8 bundle
Hard to say who is winning currently, because there is no way for know if 24+36 > 14, or the opposite... The only thing that we know, next Media Create will be close.