Ok first I am going to excuse your dismissal of the impact culture and social zeitgeist have on a people. Then I am going to point out that the Japanese culture is so very different from Western Culture that their overall view of guns is very different from ours.
Secondly, you are ignoring social structure, economic factors, historical factors, race issues, social density, the identity of the people as a single organism, and the singular identity of the individual, the differences in our law code, our social code, our tabboos, our beliefs, politics, psychological state of the people, the media, the system of government, drug flows, black market, under the table guns sales, the apathy of the people, the natural tendencies of our species etc etc etc.
All this stuff makes every single culture on this planet different in unique ways. What works with one will not necessarily work for another. If you think we are all carbon copies and react the same way to everything I suggest you invest a small amount of your time in social studies. You can take our guns, but I assure you crazy bob down the street will take a knife to someone. The crime may not be as big, but that is purely up to the imagination of Bob. Bob can take 10 minutes raid his kitchen and blow up a school. Bob can poison. The mind of a violent person is only limited by the extent of its imagination, and the social structure around it.
Violence doesn't stem from guns. Violence is enabled by guns, yes, but it is enabled by countless other factors and objects. Violence stems from us. To assume that taking all guns would be a magical cure-all is ignoring countless human factors.
We do need to limit guns. But of equal importance is looking at the people and fixing issues in our society. There is a reason why most successful species do not tolerate killing of their own. It makes for a weak social structure. Yet, we allow it, and sure as **** it is hurting us. The problem is much more than just guns.