Hmm. Lucius looks more like a genie. Are we sure he's a demon? That aside, I really like reading about contract-based power systems. Excited to see where this goes.
Spoiler:
Lucius might be a nod of ||Lucifer from Ars Goetia and the lesser key of Solomon.|| Unsure about this as ||there's also a chance that Lucius might be referenced from St. Lucius just like the other characters in the story: Ignus (St. Ignatius), Vincent (St. Vincent), Atticus (St. Atticus), Tobias (St. Tobias)||
But if the first one's correct then ||there are specific steps or rituals for you to do in order to summon a demon, and that demon will grant you anything in exchange for your soul||. But this is just mostly theories and might be disproven as the vn is still in demo