The core of that tension always feels like a question of ownership, to me. A butler, demon or otherwise, is bound by a contract of service—their entire existence is ordered around the fidelity to a single master or household. But dark supernatural orders, whether it's a hellish aristocracy, an infernal guild, or the primal chaos they sprang from, operate on a different kind of allegiance: fealty to a system, a hierarchy, a cause, or raw power itself.
The conflict sparks when those loyalties pull in opposite directions. Say the order commands the butler to sacrifice their mortal charge for some greater ritual. The butler's contract might forbid harming the ward, creating an impossible standoff. I'm thinking of Sebastian from 'Black Butler'—his ultimate loyalty is to Ciel's soul, but what if his original demonic nature or a higher demonic authority demanded he break that contract? The drama isn't just about power; it's about the violation of a personal oath, which in these stories often holds more supernatural weight than blind obedience to one's kin.
It makes for fantastic internal struggle, where the butler's cultivated precision and control—their entire professional identity—grates against the wild, often destructive, demands of their innate nature or old affiliations.
You see it sometimes in the aesthetics too; the pristine gloves getting stained, the perfect posture slipping.