The purpose of my original comment was that the US dwindles Japan in firearms, but Japanese still manage to kill themselves just fine. So it's not a strong point by the parent I responded to. If Japan maintained that decrease for several more years, I think this would be worth revisiting, but for now it doesn't have much weight.
Note that Montana, the worst state for suicide, is about the same as South Korea at 28/100k.
I say this sadly as having had a friend kill herself in High School via a gun her dad had lying around. And ya, it was a red state (Mississippi).