The so-called sun is his Great Sun Primordial Spirit.
The so-called moon is his wives and concubines.
This is a Dual Cultivation Technique specially created for his own Great Sun Primordial Spirit. Even if others obtain it, it would be of no great use to them.
A woman practicing this technique, during Dual Cultivation with him, can use the Power of Time from his Great Sun Primordial Spirit, exhaust her potential, overstretch her future, and ultimately achieve complete transcendence with the aid of the Great Sun Primordial Spirit.
With the Great Sun Primordial Spirit as the Immortal Bone, she becomes extraordinary and ascends as a Celestial Human.
But this act severely damages lifespan and potential. Even if she barely achieves Celestial Human status, her foundation will be shallow, her strength weak, and she might not even be able to defeat an ordinary Half-Step Celestial Human. At most, she can only live for a few more years before her lifespan is exhausted.
