Ok I found one-R A T E .
Person A is a royal who got turned into a vampire when they were married off to one (who only married them to gain the wealth attached to Person A), but Person A’s personal bodyguard/knight gets killed on a mission (actually set up by the vampire who Person A married, since their bodyguard was deemed a problem). But when their bodyguard died, their dying wish to protect Person A forever took the form of a demon (beings that are lower on the status scale than vampires due to having been created from human sins/tragedy/negative emotions and not ex-humans), Person B, who’s sole reason for existence is to keep Person A safe and happy. Person A starts to develop the same feelings of love for Person B that they had for their bodyguard, but tries to deny their feelings since their vampire spouse always speaks negatively of demons.