To illustrate, allow me to present the manga version of the backstory between God (the Master in the U.S. game) and Satan (Tanzra).
God's notably-finite divine omnipotence is running out - he's getting too old to be God, you see - and he needs someone to be New God. To find New God, he conducts a Star Search of humanity, finding a promising candidate in Noted Human, Satan.
(Satan is actually human, not pretending to be human.)
God takes Satan as his God Apprentice. Unfortunately, God's lofty plans to have his human bestie Satan succeed him as God are shockingly - shockingly! - derailed when Satan betrays his sterling reputation and uses his appointment to New God for evil.
Never mind game canon; we can't even get Abrahamic canon right.
(The angel from the game is actually the rat narrating the tale, as a rat is the only form God's celestial messenger can take in manga continuity, which here is less commentary by a proud rat owner and more a signal of the regard in which the artist holds the original material.)