If Japan wanted to help South Korea, what could it do?
Perhaps offer some air support, but what else? Just a token amount of ground troops?
There will be no war. China will not permit it—they have a great deal of voice in North Korea. In a one on one match South will beat North. The North just wants more aide. Omaba will give it to them too.
My money is on the ROK. Kimland has nukes, but not many, and they are going to find the ROK forces are a lot tougher than they have been taught.