Overthinking things is one of my favorite hobbies, and prettyboy demons proclaiming their lascivious desires through musical numbers puts me in mind of occultism and mystic traditions.
I notice each of the demons has a sigil motif which accompanies them onscreen during particularly dramatic moments. Rem has a got skull, mage has a serpent, etc. I have a sneaking suspicion that this might have some symbolism or ties to some real-world grimoires, like the Lesser Key of Solomon or something similar.
Are these born from real-world occult traditions? Or are these just motif used by the art team because it makes it easier to make an icon to represent each boy and brand their merchandise with?