I don't know why I thought this was a Hannibal crossover for a second but now that we're here, 100% Hannibal was an entity for The Flesh & would have attempted his own ritual if it weren't for his failure to convert Will into the partner he needed for it
DUDE
OH MY GOD
THIS IS ACTUALLY PERFECT BEST CROSSOVER EVER
I need to draw this so badly now
But hear me out
What IF Hannibal is a flesh Avatar but Will is slowly getting dragged into the Spiral and Hannibal is fighting to drag him out because he wants Will for himself. OR Hannibal is using the effect the Spiral has on him to his advantage to further influence Will and drive him into a vulnerable state where he can easily do his fleshy business (ignore the bad phrasing).
Hannibal also has strong connections to 1. Other cannibals and The Flesh fanatics, 2. Someone from The Web that he uses to further amplify his influence over the wet dog that Will is.
HOWEVER TO ADD TO THE SPICE Will is aware of the game Hanni is playing. Naturally, he doesn't want the Fleshpocalypse to happen, so he's struggling through keeping his mental state in check and also keeping Hannibal at bay. The dynamic quickly becomes a mental duel of two dark minds with intense canon-typical homoerotic undertones.