Sick

Mana core, a crystal made of concentration pure mana. Although it is called a crystal it doesn't have any form. It is located in the heart in an intangible shape. It is real yet also not real.

In Firuman, mana core is a very important source of power for the survival of civilian society against the monsters. Yet not everyone could awaken mana core. In the human race, everyone has a chance to form the mana core as long as they have enough talent in perceiving mana.

For the trained children such as nobles, they could even form their mana core early starting from the age of ten. The untrained child needs to have a great talent to form it naturally which usually happens at the age of 13-15.

This range of age is also the age where a human teenager could easily form their mana core manually as their body is more attuned with the mana.