These provocations can only go so far and for only so long.  Push the Japanese hard against the wall with a clear and looming risk of nuclear annihilation, then Kim Jong-un will regret it should Japan - constitutional renunciation of war or not - commit to a crash program to field a nuclear warhead in the megaton range.  Unlike North Korea's best efforts so far, a Japanese nuclear weapon, whether delivered to Pyongyang by aircraft or missile, is not likely to miss or prove a dud.