fantasy worldbuilding concept

elves, taken as the viewpoint species

they live for hundreds of years, aging incredibly slowly

an elf reaches adulthood at the age of around 100-150

there's another race out there, though, a strange race called Humans

they live for less than a hundred years total before their unstable bodies degrade completely

but they have terrifying, uncanny intelligence and adaptability

what an elf can learn in fifty years, a human can learn in three

because they have so little time, they exist in a constant state of chaos

frantically absorbing resources and information and evolving their minds and bodies at speeds that shouldn't be possible, and recklessly breeding before their own bodies kill them

humans as horror antagonists from the perspective of other races

unable to hear the voice of the lifestream, humans can kill other living things and feel nothing

any magic or tactics used against them they quickly adapt to and turn against you within a scant few years

and even if you do manage to claw an advantage against them, their breeding cycles being "only" 20-30 years means they repopulate faster than you can mobilize effective tactics against them

Humans infinitely more likely to sacrifice themselves for a cause

What are they giving up? A few decades?

That’s nothing compared to an elf that would be sacrificing possibly over a millennium

cities of stone packed dense with humans, less like settlements and more like insect hives