They would be yelling "Wuidehanryongdoja KimJong il dongji, Manse!" all the way it would seem--as impassioned as an "Allah Ahkbar!" Not out of the question.
I know of no air marshal system onboard Japanese aircraft and it's anybody's guess how soon the Air Self Defense Forces could scramble.
The Japanese are essentially not that good at crisis management, something big and entirely unexpected, which is very worrisome.
... and with Big Ole' China breathing down Japan's neck, meantime. What you have speculated is entirely possible. "Old" Japan would be pulling together and taking this threat very seriously; do you happen to know how "new" Japan is taking the threat? New Japan, meaning, the "everything is Rock 'n' Roll" Japan? What is the mood of the "everyday" people; and not those in official capacity, pls?