Yuyui knew a thing or two about souls now.
Given that having her soul drawn out was the means with which her memories had been recovered, and that she remembered the experience, the complexity and nuance of souls were something she had grown to appreciate.
Beyond that, Yuyui had gotten quite close to Ferex after Skullius 'exiled' her, having her travel with Replicus and Kenno's crew instead. Ferex was particularly knowledgeable about souls. He had abilities that allowed him to interact and manipulate them – like [Spirit Walk]. These abilities worked even on high-level creatures. A good example was what Ferex had done with the Cluster General, he, Skullius and Yuyui had fought on the assignment Skullius had chosen from the Guilds Association back in Genhuis City.
(A/N: Refer to Ch.484).
Ferex knew a great deal about the soul and Yuyui had seen him use his abilities to vex enemies firsthand.