A RETURNER'S MAGIC SHOULD BE SPECIAL - Chapter 202

Most likely he uses the 4 Tower to suck in all the mana from the inside of the field. So all people thats live there get their mana sucked out slowly but constantly.

Since he successfull summoned a demon in the past and sealed them in a case he most likely wants to do the Same with his godess.

Which is most likely no godess at all or the gods are evil in general.

Like demons are evil by default but some gods are the greater evil since they are neither good nor bad. But they decide themself to bei so and are quite crafty since they wont make decision on smth like inate feelings or their nature.

So they are more organized and can do more damage long term due to being able to communicate with some individuels (like the pope) and using them.

Maybe the hummunculus is the case he needs for his godess.

And maybe he even uses the towers to sacrifice everyone inside while sucking the mana out to simultanlouisy creating the case and summon her or it on the planet.

Only to seal her into the body and baaaam End Boss is there.

Maybe this individual is also the one that created the shadow worlds.

Or it was another entity of this caliber.

Maybe its all wrong but seems legit to me.