I would not say that Japan is taking an “overly”-cautious attitude toward the Kosovo question. After all, the overall direction is clear. We will in principle recognize Kosovo, and that should please the US and the Islam Nation (not that the Islamic states notice, though I'm sure that they would if we said no to an independent Kosovo). However, there are no public discussions of the real reasons for our tag-along approach; it's not a compelling issue for us. So I’m really guessing here. Having said that...
China surely has Taiwan in mind in its opposition to Kosovo independence, but I don't think that the matter is important enough to China that Japan would feel compelled to defer to its wishes if they are to maintain the current amicable relationship. The China-Taiwan relationship is overwhelmingly determined by local factors and is not going to be materially affected by the eventual fate of Kosovo. Russia, in contrast, is the state that has the geopolitical interest in Kosovo and the broader counter-status quo posture that make this a compelling issue for it. To put it another way, it is my view that Japan would take the same approach if Russia were the only permanent UNSC member opposing Kosovo independence, while Japan would afford more immediate recognition if China were the only one doing so. Of course China would have to accept it if Russia decided to drop its veto on UN accession for Kosovo, so the last scenario would never happen.
The one possibility that I did not consider in my previous post is the possibility that Greece and other EU member countries withholding recognition (but, crucially, not opposing EU takeover from KFORS) will
In the meantime, Japan should be providing humanitarian and other forms of assistance that will not offend the Russians.