Can we take a moment and sorta play out a scenario like this? So North Korea fires nukes at japan, they either hit/do not hit. What impact would this have on Un forces? Also we need to take into consideration that fallout will spread east if they target the southern portion or west if they target the northern portion.
-snip-What's next?
They wouldn't nuke Japan first though, firing missiles at Japan is just a sham to provoke the US so that when the US takes action, they have an excuse to fire a nuke at a Piece of the US, they would probably aim for the closest piece of land that is considered US Territory and then let it escalate from there, they would not risk a nuke hitting the ocean considering their "satellite" had a misfire and landed in the ocean, so they would only use their shorter range missiles to carry a nuke, and that means hitting maybe an island that belongs to the US or something.
As for the aftermath? Well there would be tons of contaminated fish...heck maybe even dead, the beaches would be unsafe for quite a while, not much but what would really matter is what island they would fire at... that is the big variable.