Herm. It seems I have been struck with the
Curse of Knowledge. Rather a lot, actually. Okay.
Weapons can take pretty much any form that could conceivably be used to hurt someone else (Shields, cutlery, slingshots, cannons, a guillotine, pistols, swords, whatever.), and are a specific type of human, originally artificial, but appearing in the general populace apparently at random after the creation of the first. They are, more or less, resonators for Soul abilities, dramatically improving the combat potential of both themselves and their partner. Both they, and witches, manifest their abilities sometime during mid/late puberty, so children could survive the apocalypse without direct harm. Witches
seem to use their own voice as a channel for Soul wavelengths, in the form of a chant of only a few very similar words. This chant will always be the same for a given magic user, but is not necessarily unique to only that one person. In the show, witches use animal chants, presumably for versatility of traits and solidarity rather than any real restriction, as magic is shown to work with "pumpkin" as a chant as well. There are other kinds of magic, focused on the creation and use of magic tools, presumably through the creation of synthetic souls, which remain without much identity, as souls are the only demonstrated power source for magic, and the soul of a human is not needed to create a magic tool, the first Weapon excluded. Golems also exist, and provide stronger evidence for synthetic souls, although at least one did have a human's soul.
There are a couple of ways a weapon or magic user (very likely a witch, as they would not appreciate competition) could survive the apocalypse. If one was in a faraday cage, intentionally or not, they could not have been harmed by a magnetic field, so anyone in a metal box or wire mesh without an opening would survive. A scientist trying to avoid magnetic interference on a project, a stowaway in a shipping container,
a chicken farmer hiding in a coop with a shotgun waiting to ambush a fox, there would be survivors, although a lot of them wouldn't be able to actually escape, what with the apocalypse ruining the ways out of some of these. Or, the character could have simply been born after/somewhat before the apocalypse happened.
Sorry for not explaining the state of affairs better. I screwed up.