Find someone whose wisdom has been taken, whose soul seems to have lost its mind but hasn't dissipated, and who's not dead—then nourish that residual soul, the part representing spiritual intelligence, with your own, using soul to heal soul.
This method isn't all that evil, really—in fact, it's mutually beneficial for both parties.
Once complemented, one side gets to be nourished, slowly regaining some clarity, while the other, having been restored, no longer faces the risk of dissipating soul.
If you use other soul-nourishing methods on top of that, both sides benefit.
Seeing this, Wen Yan finally understood why Liu Qiying dared to come clean with Wu Tingsheng.
Thinking back on Xiao Wu's earlier state, Wen Yan was certain the information wasn't embellished in any flowery way; it was just the plain truth.
Back before the Soul Devouring Beast's job change, to be honest, this method really wasn't a problem.