You may have realized that I talked to Devil, and he appeared with an incomplete soul. Allow me to correct this plot-hole.
How do I put this... That version of Devil was from the predicted future. However, the future has changed, Devil may not make it. However, that moment still exsists through paradox. Devil can exsist in that instance. Afterwards, if he doesn't make it, his future self will disappear. I know these time travel rules are odd, but they work.
Devil was originally going to tell a prophecy to the readers while they were in the void, but this was removed due to time constraints. How did be time travel? I dunno, but there's an explanation, trust me. For now, just enjoy the rest of the story.