Maybe they should make it illegal for North Korea having nukes 
It’s not up to the Japanese. Talk to the UN. They’re the ones who wrote their Constitution. The ban is left over from after WWII.
The Japanese government is elected by the Japanese people, and there is no means for the UN to affect it or the country itself whatsoever. That, logically, means that anything they do is entirely up to them, and it most certainly in no way up to the UN. (it would probably make sense to clear a big military investment with the US administration, but that’s more out of politeness toward their biggest ally. Plus, I don’t think the US would object in any way, we’re desperately in need of serious allies)
[edit] I see that Clawq just summed it up much better above.
It’s not up to the Japanese. Talk to the UN. They’re the ones who wrote their Constitution. The ban is left over from after WWII.
In recent years there has been some discussion of changing their Constitution. Now would be a logical time to do it. If a nation chooses pacifism in the face of aggression, it’s not up to us to continue to protect them.
Interesting comment I read somewhere: “These are not test firings, they are sales demos.”