Anime does not promote Satanism. It loves to make fun of it.
In every anime I've seen in the past decade that has featured a demon lord type character, the character has been placed there to be funny, to be made fun of, or to be outright defeated by another character.
Satanists get dunked so much (especially in fantasy anime) that it's almost unfair how much the scoreboard goes against them.
Also, God is not portrayed as a villain in the anime. Anime features "fake" gods as villains. People think they are gods, but in reality they are very conceited and think they can run the world better than anyone else (of course, they are all proven wrong). Most god characters in anime are either benevolent and kind, or comedic.
Nor is God more than a figure (if He were only a mortal vessel in the first place), He is virtue, teaching, principle. Anime is full of these.
God also teaches us how to overcome the darkness of the human soul, but if we don’t understand it, how do we know what to overcome? Know your enemy.
Anime needs to show the darker side of existence in order to not only tell a balanced story, but also serve as a warning of potential dangers.
Don’t mistake an opportunity to learn for worship. This is a warning, not a love letter.