that emphasized portion is salient to the conversation... order to destroy the missile should any part of it threaten to fall onto Japanese territory ...
japan is only exercising prudent self defense
just as iran does when it shoots down American drones flying in iranian air space
there is absolutely no love lost between the japanes and the koreans ... doesn't matter, north or south ... so japan is not going to refuse to defend its territory out of concern its action might provoke an attack on SK by NK
and should such an attack scenario unfold, is there a place on the planet where the use of tactical nuclear weapons might be found more acceptable