

In Kyoukai no Kanata, the hunters make a living out of selling Youmu stones,
allegedly the souls of the defeated youmu. It goes even to the extent of a
school teacher taking a leave to hunt during a particular event.

What is the use for those youmu stones after they are sold? Why are they
valuable to others?

* * *

What I am looking for is some source material reference from other media (I
only watched the anime).


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2014-07-21T20:21:47.150
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beyond-the-boundary
What are Youmu Stones used for?


Youmu stones serve as a proof of victory of Spirit World Warriors over the
Youmu. It's unknown what they are useful for except that. Each stone has its
own "aura" detectable by Appraisers, who can tell how powerful the defeated
Youmu was. Think of the stones as experience points earned in a fighting game.
The more you got − the higher level you are, and as a result, thought of as
more powerful by other Spirit World Warriors.


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2014-07-21T20:29:12.243
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There isn't really too much source material on the youmu stones besides the
anime. However, we see that the youmu stones are brought to appraisers to be
sold as a proof of victory over a youmu. However it's never explicitly
explained as to what use the stones have.

Based on the Kyoukai no Kanata wiki:
<http://kyoukainokanata.wikia.com/wiki/Youmu>

> The similarity among all youmu is their tendency to manifest an ore-like
> stone that contains the powers of that youmu when slain.

If this is the case, then the stones could be being used as a medium to create
the different powers of all of the Spirit World Warriors. This would explain
why stronger youmu that are slain have higher value stones.


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2014-07-23T19:21:55.967
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I will build on
[FatalSleep](https://anime.stackexchange.com/users/3034/fatalsleep)'s answer:

> [The similarity among all youmu is their tendency to manifest an ore-like
> stone that contains the powers of that youmu when
> slain.](http://kyoukainokanata.wikia.com/wiki/Youmu)

In the anime, it is shown that [Sakura
Inami](http://kyoukainokanata.wikia.com/wiki/Sakura_Inami) can use Youmu
stones to empower "her" spear-like weapon.

Given  
**(1)** that the stones have the powers of the youmu and  
**(2)** this use of the stones shown on screen,  
we can infer that the stones could be used to empower/create magical items.

The barrier sticks, the charms and several other magical artifacts from the
Kyoukai no Kanata universe could be made using the power from those stones.

As magical ingredients, youmu stones would be very valuable and highly sought
after. This would justify the Ikaishi income, the wealth of some Ikaishi
families and the economy of the Youmu stones market.


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