Used to test ones soul realm by injecting it with a bit of power. It is primarily used to determine the soul force, but if one uses a fresh one that has not been used by another, more detailed information about the soul form and attribute can be determined.
Below are the currently known soul crystal ranks and the level of soul force it can measure:
|Rank||Soul Force||Cost (Demon Spirit Coins)|
|Primary||0 - 499||1,000|
|Intermediate||500 - ?|
Note: Chapter 51 says the primary soul crystal breaks at 600, which conflicts with the 500 stated in Chapter 12. Which one the author intended is not yet completely clear.