Ao no Shigyaku Midori no Higyaku

The protagonist gets to view the story from two perspectives, one from the POV of a female master and the other of a slave. The story takes place in a kingdom where slavery is legal. The wealthy nobles buy these slaves as jewels to embellish themselves with or as toys to fulfill their desires. Every person takes the law as a given, and accepts these actions as facts. That is why commoners work their very best to avoid lowering their positions to slaves. In such a scenario, you stand out as the odd one - you don’t treat slaves like slaves, you don’t stoop so low in front of your master either. And that is precisely why you will receive an extraordinary ending.