LOOKING FOR A STORY OF ROMANCE BETWEEN A SUB AND HER MASTER.
Here's a nice one to start the ball rolling:
'Here's the Thing...' by Tedbiker
AJ
MWTB's Tired of being the nice guy. Don't let the title fool you,,,she's better at being the sub than he is the master...
https://storiesonline.net/s/41241/tired-of-being-the-nice-guy
When you say 'slave' are you talking about the submissive person in a relationship, or a person 'owned' by another, as in the pre-Civil War South in the USA?
If it is being owned, Uncle Jim's 'Slave Girl' stories almost all feature a romantic relationship.
https://storiesonline.net/series/616/slave-girl
How about "The Collar Around the Heart" by Old Softy
https://storiesonline.net/s/52848/the-collar-around-the-heart