[After walking the cultivation path dozens of times, you are now experienced in your initial cultivation.]
The Xuanzhao Realm is essentially Qi Gathering, where you condense a True Essence Seed in your Dantian.
Activating the True Essence Seed allows you to perform some simple magic.
The Enlightenment Realm involves using this True Essence Seed to cleanse the body, most notably creating unusual phenomena in the eyes, enabling you to see things invisible to ordinary people.
Zhao Fu crossed two realms and directly stepped into Fusion.
The so-called Fusion Realm is merely the complete fusion of True Essence with the body, permeating every part of the flesh.
In other words, it's like marinating the body with True Essence.
However...
In later generations,
The Qi Refining Realm is directly about condensing True Essence.
As True Essence expands, it fills the meridians from the Dantian.
