Speculation that China may begin unilaterally drilling in a gas field, the ownership of which is disputed with Japan. And that Japan may therefore follow suit.
All this is contingent on whether Beijing is lying or telling the truth about the purpose of some heavy equipment they've moved into the area — which it claims is simply for maintainence work.
UPDATE (Sep 19/10): Starting to look like the Chinese Communist government was lying. Aerial reconnaisance photos of the machinery appear to show that it's drilling equipment.
UPDATE #2: Japanese Foreign Minister Seiji Maehara is quoted as saying, "Territorial disputes do not exist in this region."
In your dreams, pal. Wherever China's borders lie, there's a dispute to be had.
UPDATE (Sep 20/10): Rather than aping China's infantile behavior, Japan may instead take the case to the International Tribunal for the Law of the Sea. Good for them.