I got a master who wants to turn a slave into his assistant. (MxF, looking for F))

After watching Rising of the Shield Hero for the second time, I wanna try something like it. You don't have to know the show for it tho, so no worries there. Let's get to the plot:

My character needs an assistant. He makes medicine, but doesn't trust someone he could pay to do the work. Who is to say they might not steal his work? So his idea: He gets himself a slave. They are bound to be loyal (by magic means, usually).

The bigger idea behind it that my character is definitely not someone people would trust on first sight. He looks odd, has an ego, and has a big mouth. Yet he does know how to make medicine and sells helping products to people rather than poisons to adventurers and criminals. So maybe all he needs is to show that he can be kind and caring, despite how he looks and can act.

Plot wise it would mostly be about him caring for her at first, then introducing her to his work, and it could later turn into quite a few things. Some ideas from my side:
-A revenge story if that is up your alley. After all, not many people willingly become slaves.
-Her inspiring the idea in him to let go of what eats at him and start a new life.
-Him training her to be a heroine for the sake of saving people... and a higher status.

-Or fukkit. All at once?

And the character I would like to use is this one:

If anyone is interested, please let me know. I'll reply ASAP.