You Xi Wang sat on the boulder with his eyes closed. The first thing he had to do before recasting his skin was to shed off the old one. The process was unlike something he had read in novels in his old life.
The novels showed how people will temper the skin inch by inch in such processes. However, here, the process of casting the tempered skin was very gory. He will have to cast a scalpel with the spirit energy. This scalpel must contain the purest of the energy that a practitioner can refine and then slowly cut off his skin leaving nothing but the skeleton.
No methods must be used to avoid the pain, the genitals were to be removed as well and then recast with the spirit energy. Imagine the guts it will take for a person to do that. However, the genitals can be avoided.