Well, try thinking back to the last time China and Japan were ever on good terms. That's probably why. They very much dislike each other, so it makes for a good (semi-realistic?) plot.
lol. Your reply just made me want to reread okane ga nai.
Another similar plot like this is from Viewfinder where akihiko, asami and feilong have a threesome.
that was one hot chapter.
God yes ლ(´ڡ`ლ)
Why does gangsta yaoi genre always have Chinese Seme vs Japanese Seme fights over uke???