Comment by Manghuwa on The Heavenly Demon Wants a Quiet Life - Chapter 23

@Manghuwa he can absorb all energies...in his past life, he just absorbed them without reservations  both pain,anger,fear,joy leading  to qi deviation at the end but now he's carefully utilizing it's energy.. negative is violent and positive is calm..and he can absorb all but he prefers positive since it's essence is stable

@Manghuwa He is learning how to purify the soul extraction.  He can focus on a single thing and pull that out, leaving behind a rarified soul which improves the body as a result.  Think of all of those "impurities" that you see in other manhua's that get expelled from the body and then think of that as what he pulls out.  Those impurities have energy to them and are also tainted with the overall condition of the soul.  He gets a tiny portion of the nature of their soul while refining it for them and extracting the energy from the impurities for himself.  If done correctly, everyone wins.

He can also forcibly extract the entire soul (or half of it) for various horrible effects.