In the Cultivation World, when a Foundation Establishment Cultivator's cultivation reaches the late stage, they could refine Heaven and Earth Spiritual Fire and store it inside their Dantian.
Refining Spiritual Fire is preparation for ascending to the Golden Core!
At the Foundation Establishment Perfection, if a cultivator could merge the Heaven and Earth Spiritual Fire into their Spiritual Power, successfully imbuing their spiritual power with some characteristics of the Spiritual Fire, their chances of ascending to the Golden Core would significantly increase.
Depending on the Five Elements, the Heaven and Earth spiritual items that cultivators refine also vary.
However, unlike ordinary cultivators, those who have practiced the Golden Core Technique, upon advancing past Foundation Establishment, cultivate spiritual power that is more refined than ordinary spiritual power.
