Almost all of humanity either died, or was forcibly de-evolved into mole people. The reason that you see this pocket of Japanese who still are living on, is because the system they designed and conformist culture allowed for a small, primitive society to exist as a remnant.
That still doesn't mean they're the only society left. There was a story about fiends and it involved India. It's not just this society with cantus users, there are different nations. And keep in mind you said "most" so that means more than half of humanity died off. More than 50% of humans. That could be 51,52,53,etc. I don't think the anime EVER mentioned an exact amount of humans. So there could still very much be billions. Ill be nice and assume that 75% of humans died. That's 5 250 000 000 people. Even then, it's unlikely that this is the ONLY place with cantus humans.
No. Look at modern society. People kill each other with guns. There's no "shield gun" that blocks other guns. Sometimes powers are skewed in favor of offense. That's how it works in SSY.
Completely different. A gun is an external object, their cantus abilities are a part of them. A more accurate representation would have been people using their fists or legs not a gun.
They did occur, and there was no death feedback back then, so humans destroyed each other. Death feedback was basically an evolutionary engineered response to protect what little remained of society.
Which could still be billions of people because for some odd reason, the anime, I THINK never stated the amount of people left. And what's even more interesting is that without a doubt, Im completely confident in the head-canon that the only nations that would have survived were the 1st world countries, not all but some. It's impossible shallow the fact that only this society remained, again, poorly put together society.
My impression of SSY is that humanity is in a post apocalyptic state where the human population is a tiny fraction of what it once was.
Ah, so it was never stated, the amount of humans left right?
The whole later part of the anime is an all-out war where the mole people rise up and try to exterminate the humans.
I can't really call senseless killing and if anything easy killing "action"...
Action would be like DBZ,one punch man, boku no hero academia, K return of kings, World trigger, that's action. Killing defenseless people isn't action in my book. It's like calling a serial killer movie an action movie, like no...