Compared to the Soul Searching methods of the Celestial Mother's Birth Profound Light and the Heaven-Mending Skill, transforming souls into Banner Spirits with the Myriad-Soul Banner could also achieve a similar effect.
However, the latter method had a flaw: the spirits lacked autonomy.
With the exception of Banner Spirits like Chen Xin'an and Progenitor Tingyou, who had willingly entered the banner while alive, most Banner Spirits would only act on commands.
Therefore, Soul Searching a Banner Spirit could only be done through a "question and answer" process.
But this could easily lead to a catch-22.
Lü Yang: "Why didn't you tell me about this?"
Banner Spirit: "You didn't ask."
Lü Yang: "How could I ask if I didn't know about it?"
Banner Spirit: "If you don't ask, how would I know that you don't know?"
And then things would grind to an awkward halt.
