Hmm, I like your ideas. It'd be set it in a modern, fictional city similar to New York, because I have no idea about New York/Tokyo. XD

[quote=Quatro]
Maybe label it "witchcraft" but the general scope would be vast. Shamanism, voodoo, exorcism, and magic could be considered various styles.
[/quote]

I was thinking similarly. ^^

[quote=Rowdyruff]
(solely because I enjoy real life "faceclaims"/appearances more than anime and I'm not really aware of the asian celebrities of the world!)
[/quote]

I'm the opposite. >< Perhaps I'll allow descriptions in appearances only. 

Should the 'demons' be other supernatural beings? Like vampires, werewolves etc. Or should they be different ranks of demons of the same type? Like, maybe low-level demons would be winged creatures that just cause some trouble and higher level ones would be ones who look more like humans, perhaps personifications of the seven deadly sins, and then there would be a 'Demon King' ruling them all.