Japan's lack of homicide in general is more cultural than anything else. Homicide in general, and gun violence in general is closely connected with culture in many regions If you don't see culture as impact, I'd ask you to compare El Salvador to the US.
In the US, there are 120 guns per 100 people. In El Salvador, 12 guns per 100 people. That's 10x more guns per capita in the US.
In the US, the homicide rate is 5.3 murders per 100,000 people. In El Salvador, it's 61.8 murders per 100,000. That's almost 12x the rate.
So El Salvador has 10 x less guns per, but 12x the homicide rate.
In the US.... high homicide rates have a pretty strong correlation to politics.....St. Louis and Baltimore, both have El Salvador level homicide rates. Detroit, New Orleans, Baton Rouge, KC M, Cleveland, Memphis, Newark, and Chicago round out the top 10 and are between roughly 5 and 8 times the national rate. All are Dem strongholds..... Perhaps they should try a different party?