Affinity

The body serves as a vessel, enabling existence. The soul bestows consciousness, imbuing life with awareness. The dantian functions as a center for energy accumulation, while the meridians channel and circulate this vital force. Blood Essence embodies vitality, longevity, and inherent potential. Affinity, however, grants one the qualification to interact with the world.

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The body, soul, dantian, affinity, meridians, and blood essence are necessary for any cultivator. Perhaps if one solely focused on Body Tempering, a dantian wasn't needed, but even they still used it to some extent. 

Messing with any one of those could bring about unexpected consequences. 

For example, those who absorbed beast blood essences incorrectly might deform, turn into raging monsters, or die on the spot. Even doing it correctly but using an incompatible bloodline wasn't ideal.

Doing so could also hinder one's potential.