Mental Energy!
It was something that he awakened through the Soul Cultivation Technique. Even its creator, Heavin, hadn't guessed that Mental Energy could be awakened when one practiced it. It was a pleasant surprise.
But surprisingly, in this world of sufferings, Krune awoke it in him. The moment he did so, he obtained an enlightenment related to Mental Energy, understanding its essence.
'It's an energy of the mind, undetectable normally because not everyone can harness the mind.' He took in a deep breath as he thought this. 'The reason practicing Soul Cultivation awoke Mental Energy was due to the development of the soul acting as a force on the mind to condense the mental waves, producing Mental Energy.'