The AEA Zeus can fire a .72" projectile at 900fps. Within its effective range, that's a big-game rifle.
I can appreciate the information being provided in this manga, as it both educates and helps the reader realize there is much more going on than just "guns bad, m'kay."
It's also interesting that city people there have the same attitude as here, in that critters are cute and cuddly. unfortunately they are less so when you hit one with a car, a genuine danger and destroyer of crops and property, and risking their own local extinction due to diseases, all because they are over-populated.
Like it or not, Humans are part of the ecosystem and food chain in most places we inhabit. If everyone in my state, for example, were to stop hunting deer, that would be 213,000 deer (this past season alone) that would be alive to breed. We're looking at an exponential growth year to year if all hunting stopped.
Fortunately careful management ensures that an appropriate number are hunted, home freezers and even the less-fortunate have a supply of healthy meat, and the training of self-sufficiency continues.
If the worst-case plausible scenario ever happens, some people can and will survive.