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There's also been all these hints and lore about demon lords. "How to not summon a demon lord" and "That time I was reincarnated as a slime" both have the theme as well as similar procedures. The followers are called "fallen" and they all give off purple energy. The difference is explained as demons having endlessly recharging magic, it just flows through them, contrary to regular mages who have to recharge after using it.

"Dawn of the witch" has an mc with this same ability.