It was not until I read Jeffrey Lewis's wonderful (as always) trip down a side road of China's nuclear weapons programs (Link) that I understood there could be more to China's hopping up and down about Japan's possession of plutonium, both in weapons and reactor grades (Link)
than just spiteful, hypocritical mendacity.
Not a small part, if not indeed the majority, of China's griping could be out of simple envy.
In terms of separated plutonium, Japan is the superpower in Asia. Big, bad China, by contrast, is the minnow. (Link)
That Japan has done nothing with its plutonium except burn it in its civilian nuclear power reactors in MOX form seemingly (likely) does not affect Chinese sentiments on the issue.
Later - Up-to-date comparisons of fissile materials held by various countries. (Link)
Original image of Rokkasho Reprocessing Plant courtesy NBC News.