Well, I have a very unusual idea for a slave. It's semi-fantasy in the aspect that the slave has some sort of psychic powers: the ability to influence thoughts. Now, the slave decided to use this. My idea is that the slave comes to have feelings for the master/mistress. It can be either romantic or flat out lustful. The master/mistress, however, doesn't share them (either because he/she just not interested or her/she don't treat his/her slaves like objects.) The latter would be why my character'd reasoning, if I ended up being the mistress/master. I don't know which role I'd like to be, so I'm leaving it open. I will play either. Now, back to the idea: I'm not saying that this means the slave can rape the master/mistress. Just influence him/her to pay a little "special" attention to him/her, which kind depends on your character's motives.