Link to episode, relevant bit is near the beginning.
To summarize: In America, any Nazi asshole with even the slightest murderous intent can get a gun pretty easily and then use it to kill a bunch of civilians in a mass shooting.
This is in contrast to Japan, a place with very strict gun control, where it's far more difficult for said Nazis with murderous intent to get their hands on a firearm to act out their fantasy. So what happens is those Nazis, even if they kinda want to kill, are still too lazy to go through the arduous process of getting a gun to do so and are more likely to just stick to the far easier option of posting on 4Chan.
So those people in Japan who do want to get a gun bad enough aren't going to "waste" it on a bunch of no-name grocery shoppers or whatever, they want all their effort to be "worth it", so instead they do targeted attacks on high-profile individuals, most likely politicians, like Abe.
So that's why in America we get plenty of mass shootings, but very few political assassinations anymore.
I'm in Britain, and I'm not saying they shouldn't mitigate the damage. There is absolutely a difference between what a gun with 2 shots in it can do compared to a gun with 30. The only reason I bring these things up are that it is a more valuable discussion to be having, these problems are caused by capitalism at its worst in the richest most affluent country in the world with the highest amount of resources to deal with them. The "guns should be regulated" issue has no economic, societal or class analysis of these events, it boils things down to symptom and treatment instead of material cause which is where communists should be.
With that said I don't know if I would support it anymore. Seems more like they need as many guns as they can get for the fight against fascists that's coming.