Whatever the reason is, by witnessing this event, Ye Xiao at least understood that there is a small part of the Demon Emperor's soul hidden in the Dark Source Crystal. And he wants to take over his body in the future.
As for when?
Ye Xiao guessed that it must be when he comprehends the Dark Force from the Dark Source Crystal.
A warrior could only comprehend any Force after stepping into the Chaos Spirit Saint Realm and becoming a Minor Saint. And Ye Xiao has to become a Minor Saint within 5 years otherwise he will die.
Dark Source Crystal was already affecting his Chaos Divine Sea. As long as his Chaos Divine Sea completely turns dark, and he would have yet to become a Chaos Spirit Saint, his soul will be corroded by the darkness of Dark Source Crystal and he will die.
However, if he becomes a Chaos Spirit Saint within 5 years and starts comprehending the Dark Force, his body will be attacked by Demon Emperor who intends to seize his body.
