People will attribute masculine and feminine gender to ‘master’ and ‘mistress’ respectively, but I think master would be the ‘neutral’ pick here.

Or you can shuck the dynamic with: owner, divine, ruler, royal, liege, or any number of ranks with which you attribute subservience! :3

Oh yes, calling me “liege” is going to be amazing once I stop laughing.
Whoever uses that one needs to put on a British accent whenever they use it, even in the middle of sex. Sorry, it’s a requirement, I don’t make the rules.