It's a long story.
(ok not that long)
Basically, when I joined, I caused a bit of an upset that got Mizal mad at me. Master was kind enough to place his protection on me after I gave him some fan art of The SHAME Pit. (Didn't know that would happen, but yippee! :D) So, to show my respect, I asked him what he wanted me to call him, to be respectful. Master was one of the options and I felt it was suitable. So, until I have earned the right to call him what everyone else calls him, I shall call him Master. :) (Also, he likes it)
...And since you are his beloved Daughter, is there a name you would like to be called by me, as a sign of respect, and because, as I said a little bit ago, you are my boss? :)