Beside, there's the matter of how they'd use their bombs. A large bomb deliverable by bomber is useless to NK since their bombers would get blown into pieces the moment they cross the DMZ. And I don't think they'd have those bombs anyway, for technical reasons. In Iran's case, having such a bomb is much more probable, and it's true that their bombers have a higher survival chance than those of NK since the countries around Iran don't have the same kind of technology as the ROK and won't necessarily shoot on sight anything that comes from Iran. Still, where would they use an a-bomb? Their bombers don't have infinite range. And then everyone would be on their asses.

As for warheads deliverable through missiles, that's a bit more of a problem. In Iran's case, I doubt there ever was a gun-type device built small enough to fit on a missile before, which is much more likely to be used than an implosion device as they have uranium and not plutonium. Gun-type devices are much, much simpler than implosion devices, but no one usually bothers with them for other reasons, so I'm not sure if the reason a small one has never been built is because there's some technical challenges or simply because no one ever saw the use. I'd tend towards the second option myself, meaning Iran could get a bomb on a missile, likely something like their Shahab-5 or -6.

As for NK and nuclear missiles, I've already pretty much gave my opinion in another thread. They know full well that a weapon deliverable by bomber will be useless, as I've said above. More likely than not, from the start of their nuclear program they've worked toward a design small enough to fit on a missile. Whether they have a working one or not right now, there's no way to know, but it would essentially be a matter of time before they do as they already have plutonium. Assuming they did have a bomb, then they'd still have to choose a missile. That's more or less of an issue if they want to hit South Korea. Anything in their arsenal can have a warhead near 1000kg, and the range isn't an issue. Any of their SCUD improvements will do. Or they could use a Nodong or a Taep'o-dong 1 if they wanted to hit Tokyo.

Of course I don't think it's necessary to say that launching a nuclear missile will result in the sky raining fire over North Korea. That aside, before they could actually launch their missile they'd have to make at least one test to make sure their warhead works as it should, and since no crater has appeared in NK lately, we should be fine. That's not the case for Iran though, since a gun-type device is much simpler and much more likely to work.

i thought japan could not strike anyone again since wwii with some kind of treaty

Japan signed a treaty that limited the size of its naval force.

And yes SK has the tech, but tech won't save you from tons of bombs and shells. Lives are going to be lost.

Japan's navy is actually one of the most capable in the world. The treaty they signed to reduce their navy was actually pre-war.

The Japanese Constitution doesn't allow them to field their military in a non-defensive action. Not only that, but the sentiments of the Japanese citizenry wouldn't allow much of a military buildup to begin with.

It's not even a matter of numbers. The ROK and NPK only have a 300,000 man difference between them, and South Korea has a reserve force numbering 5 million. Not to mention that the North Korean army is a bunch of poorly trained, malnourished farmers that spend more time tending to crops than playing soldier.

Well, I hope they finish making Ergo Proxy before all this nonsene happens.