I hate to say it - but North Korea will nuke Japan before they hit us. Japan and North Korea have been rivals for a lot longer then us........To attack us would be idiotic, we are the worlds largest fighting force - it would be like walking into a tigers cage......
Japan on the other hand has not ever really gotten it's military built back up since the second world war, and would be an easy, satisfying target. We would also be hit if Japan gets hit due to all of the commerce that we use from Japan, not to mention the military bases there. For them to launch nukes at us - it would take a very insane person to decide to do that - look at what happened after pearl harbor, and we are much better to counter-strike now then we were then.
http://www.cnn.com/2006/US/06/19/nko...ile/index.html