Worldbuilding snippets: magical anus smell
The human world is different from the demon world and the fae world in that it has no external magic. External magic refers to the magic floating around in the ether, which a magical being may tap into. (This is as opposed to internal magic generated within the body of a magical creature, which it can draw upon to perform its magical abilities.)
However, this isn’t strictly true. Our universe actually has the same amount of magic in it as the demon one or the fae one. What makes ours remarkable is that it is vast. Our universe is so big that its total magic is spread out enough to be effectively zero at any given point in space.
Humans do possess a nonzero amount of magic, and it is the magical anus smell. If you scrounge your fingers around in your buttcrack through your clothes, some of the smell will somehow transfer to your fingers, even through multiple layers of clothing. This is physically impossible and the process is entirely magical.