The prospect of increased defence spending by Japan presents a host of challenges for China. In the longer term, they will be strategic and diplomatic, but more immediately it is proving a test for China's rhetoric.
Seemingly as a matter of course, mainland scholars warned recently against any steps by Prime Minister Shinzo Abe's administration to boost defence budgets.
The controversial US strategic "pivot" back to the region has been similarly contested by Chinese officials as outdated thinking and further evidence of Washington's habitual "cold war mentality". Significantly, the core of that pivot remains the formidable and decades-old US military presence in Japan. That includes, of course, the 7th Fleet at Yokosuka near Tokyo, buttressed by the USS George Washington - the only US aircraft carrier permanently deployed outside America.
While Beijing has formally acknowledged the contribution of the US to regional security, it bristles against activity close to its shores and is increasingly sensitive to anything that smacks of containment.
Any future drawdown of the US presence, particularly in Japan, would undoubtedly be met with dry eyes in Beijing. As one Chinese naval official put it to brass from the US navy's Pacific Command during a private gathering a few years ago, "you look after everything in the Pacific east of Hawaii, and we'll look after everything to the west".
The potential for a reduced US presence should not be forgotten, given the ongoing questions about Washington's ability to sustain its naval reach.
And there is the knot for Beijing. Any future reduction in US forces is likely to see an increase in Japanese defence spending - something Washington has, after all, long pushed for.
So how can Beijing secure one outcome while limiting the other? Can it realistically expect Japan - for all its pacifist constitution - not to want to boost its own defences? And what can it do to nudge it in that direction? Undoubtedly, it will require adroit diplomacy and nimble footwork on the public stage from generations of new leaders, starting with the incoming administration of Xi Jinping .
Recent months and weeks have seen rather more blunt rhetorical instruments from Beijing, however. Coupled with a new intensity in China's willingness to assert its sovereignty by both word and deed, it is clear that Beijing risks feeding another outcome - a simultaneous expansion by both the US and Japan.
A more robust Abe regime backed by hawks in his Liberal Democratic Party may prove too tempting a target for Chinese propagandists when the home fires of nationalism need stoking. But it is hard to see how it serves China's longer-term interests.
Underpinning such scenarios is that Japan's "self-defence force" is not to be dismissed lightly. Its diesel-electric submarines are some of the quietest anywhere and it boasts other state-of-the-art air and naval assets - despite budgets in recent years that have rarely seen more than 1 per cent of Japan's gross domestic product pumped into the military. And its long wary public seems to have an appetite for more.
Greg Torode is the Post's chief Asia correspondent. firstname.lastname@example.org