Being a weapon is a matter of blood now, so it runs in families. There's maybe one weapon in every five thousand people around the world. [he thinks for a moment, on how to explain this.] Eight hundred years ago, the heretic Witch, Arachnophobia, created the first Weapon by fusing the soul of a Witch and the soul of a human being with a weapon.

Meisters are humans with a large amount of soul wavelength. There's a bit more of them than Weapons, since they're actually normal human beings to begin with.

Only Witches can use magic. You need to be born a Witch to be able to, so...