Man God doesn’t exist in the world and doesn’t have mana. This’ll eventually get explained but still

spoilers

Man God exists in the “center” of the Mushoku Tensei world, someplace you cannot physically reach. That is to say Man God in effect exists in a separate non physical space from the world Rudy inhabits. Teleportation magic actually passes you through this space meaning that’s the same white void.

Man God’s only form of interaction with the world is looking at it, looking at the future, and talking to his apostles in their dreams. He isn’t anywhere near all powerful, and to

spoil his drive

is scared of being killed by Orsted who he’s unable to see the future of. Man God can however see his own future, which is one where Orsted kills him.

Man God basically has a very advanced form of Rudy’s eye of Foresight allowing him to look centuries into the future. Worth mentioning he’s a huge manipulator. While he lied about everything “working out” if he didn’t go to help Paul he was being truthful about Rudy getting with Linia and Pursena. Roxy would have survived but wouldn’t ever meet Rudy again which is good since Man God doesn’t want a child between Rudy and Roxy to exist