Billakin, was the name of the mineral contained in the heart of the Brully Race. To be exact, the material forming their Spirit Container was called Billakin.
The Brully Race was the sole race on Sumatra with a mineral-based Spirit Container.
Billakin, when built into a Human Avatar by a Free Human, granted the user the ability to forge Spirit Weapons out of any material of their choice.
Primary Nature–Spirit Smith!
Thanks to this property, a Brully could condense a Billakin hammer, treat it as a Spirit Weapon to hammer their arms, which is how they change the arm's shape.
Also, during this process, if they were to sprinkle a mineral, there is a possibility to transform the hand into a Spirit Weapon, able to fully unleash the effects of the respective mineral.
This process could only succeed if they hammer the mineral in a certain manner. This certain manner is the way the mineral could interact with Prana and unleash its effect.
