Preparation and sorrow
Demons used demonic energy, which is based on negative emotions like anger, greed, fear, wreath, etc.
They form the core based on these emotions and use demonic magic with its power.
Demonic magic is more fundamentally powerful than human magic as it focuses on destruction and chaos.
Their cores contain this concentrated demonic energy.
A demonic core, though corrupted, is an energy core at its base.
As one type of energy can be converted into another, demonic energy can be converted into purified energy with different methods.
It's not Mana, Aura, or anything similar but the same demonic energy without corruption.
As my Mana core stores Mana and my subconscious mind will store Aura, this demonic energy which is purified has to be used in a way it increases the density of one of them in surroundings.
I could gather more Mana with it inside this cave and practice breakthrough to (tier-2).
As for Aura... it was a different and complicated topic.