I think Japan will go through. Out of all the Asian teams, Japan have impressed me by far the most so far.
I hate their coach, he irritates the shit out of me, and due to my fantastic ability to dislike things/people indiscriminately, simply his face pisses me off. I also dislike how he talks big often.
But that being said, Japan have played really fast, modern and entertaining football, and though I have no personal attachment to either of these teams and don't mind who goes through, I predict Japan to win 3-1.