I'd probably start from Germany. Why China? China is one of the ancient culture/civilisation and practically the only one left which is still powerful enough as a whole nation. Persian, Mesopotamian, and the others have all gone. So I'd like to visit it at least once in my life. Moreover I've been learning chinese and I'd like to practice it somehow :-D.
About Japan...I have some friends who have lived there for a couple of years and told nice stories about it, so I'd like to personally see it as well.
The first thing I'd do in China would be trying to taste all the authentic local cuisine... especially from the street stalls :-D
And then enjoying the scenery as well as the culture heritages of course.