Japan is with U.S.. China and Russia lean heavily toward N. Korea. S. Korea is frequently on China's side.
As for paying for whatever goodies N. Korea may get, S. Korean government is happy to do it, because they want to make a big political splash out of it in front of domestic audience. China will pick up the rest. U.S. contribution in monetary terms would be nominal.
They know they are ground zero, and with a credible retaliation from Japan, they just want to kick the can down the road.
Maybe the US has just used the proxy of Koizumi here? Perhaps we are finally reaping the benefit of a true (for the moment) ally in Japan?