@Psychronia
As far as I know it is not exactly that.
Demon King = devil = é”王
devil / evil spirit = é”
One way of saying "magic" in Japanese is
"magic" as in "witchcraft / sorcery" = é”法
So this term for "magic" just includes a term for "devil / evil sprit".
Hence "é”王" does primarily mean "demon king" / "devil" and might be able to mean "magic king" in a derived way depending on the context it is use in.