it is worth noting that China voted to slap NK, I am not familiar with that in the past. China is a bit grumpy that NK is migrating Japan out of its self-imposed pacifism (and US reliance).
China has issues with the US, despises US power in SEA, loathes the notion of a reunified Korea ala the Germany model ... but in any and all events is much more comfortable with the US than they are with a more militarized Japan.
Think about it, if I was China I would be rather cross if my welfare obligation prompted Japanese militarism.
I'm with China on this (Japanese militarism). While the US is certainly capable of belligerence, on a historical scale when measured in terms of power and capability the US generally treats world power states with a modicum of respect.
China is looking at India, the Koreas, the US, and Japan, ... one could imagine they are concerned. The NK leadership sees that they are dead (or are heading there) finally lost a critical support vote from China on sanctions (a Chinese appeasement of Japan?) and I am inclined to think that all parties are looking for a resolution that somehow opens up NK (that is what China wants, they want NK to be like China, open but authoritarian), Japan (and likely the US and India) wants NK to be the next unified Germany, and there lies the conundrum.
NK is stoking Japanese militarism, the state is entirely dysfunctional, the patron wants a replicate, and the subcontinent continues to yearn for democratization of the Elephant.
Obama is the right guy for the job for this ... just take it easy folks.