Japan isn't the same as the United States. We don't want to be the same as Japan, because to do so would be to give up what this country was built on. We have always had firearms and our constitution says we SHOULD always have firearms.
Nevermind the fact that we have millions more guns in our country -- making guns illegal after they've hit such a penetration level would be impossible.
Japan has forbidden the keeping and bearing of arms by normal subjects since 1588; the collective guilt based controls that followed during the Shogunate were sufficiently hideous that I really can't see any utility in comparing the two nations in these areas.