Their deaths show how different from humans they actually are.
Summary:
- In Frieren, demons crumble into dust when they die.
- This is because they’re mostly made of mana.
- This sets them apart from humans and other intelligent races.
In Frieren: Beyond Journey’s End (Sousou no Frieren), demons are a race of highly intelligent beings that pose a threat to humans.
The Demon King was defeated by Frieren and her party, but the demons themselves are still there — and one of their leaders, Aura the Guillotine, was defeated by Frieren in one of the earlier arcs of the anime.
As we can see with some of them, demons crumble into dust when they die — they don’t leave any corpses. While the reason for that is pretty simple — they are (mostly) mana constructs — not many fans put two and two together.
They crumble into dust because they’re made of mana
When demons die, they dissipate back into mana. This may also imply that demons can be born from mana — as they are not “alive” in a traditional sense — and explains their long lifespans (at least as long as those of elves).
There’s more to it than that. First of all, this isn’t just about demons — mana is the reason many of the monsters exist. It’s currently unknown how the biology of monsters in Frieren works, and that includes demons, of course.
Demons are still monsters
Some viewers have accused the anime of being too harsh towards demons. After all, they’re a humanoid race, but supposedly, every demon is evil and cannot be trusted.
That point of view would have made sense, however, if demons were human-like in any way — which they aren’t — and the fact that they’re made of mana is another proof of that.
This, essentially, puts demons on the same level as other monsters in everything but appearance or intelligence.
They’re still a lifeform that evolved to look as close to humans and are incredibly intelligent — but ultimately, they’re more monster than human. Humans are their natural prey, and you shouldn’t really feel bad for the demons.
So what’s the point of this?
As for why this is a thing, fans can only speculate. Perhaps it’s there to show how different they are from humans and elves and to make the viewer understand this difference. There’s also something cool about showing them die this way.
Ultimately, it might not even mean anything, but that doesn’t matter — it’s still a cool fact that shows an important point about the enemies in the series.