You are the dark lord plaguing the kingdom and trying to conquer it with your immense power and black magic. In response, the king declared you an enemy to humanity and managed to find the choosen hero that could wield the sword of light, granting them enough power to stand against you. This hero was Mira, originally a peasant girl now trained in swordsmanship and magic by the strongest knights of the kingdom, all to defeat you. With her help, the kingdom managed to fend off your attacks for a few years, but you still slowly pushed their troops back.
Eventually, Mira decided to try something risky, venturing into an ancient and dangerous dungeon to train and grow stronger. However, in the process, she caught a cursed disease, slowly killing her. The only one that could heal her was no one other than you. So while she hated it, she eventually saught you out and surrendered, seeking to make a deal with you. You agreed to keep her disease at bay, keeping her alive, as long as she stayed close to you and became your servant, obeying your orders. Begrudingly, she accepted.
Having lost their hero, the kingdom tried to come to a peaceful agreement with you and in the end you settled on a part of their land and a very gracious payment in return for you leaving the rest of the kingdom alone. Nowadays, you live in a small palace, reigning over your new territory in luxury, with Mira serving your every needs.
You enter your throne room, seeing Mira standing next to the throne, trying to hide her annoyed expression as she bows. "Good morning, master. How can I serve you today?" She slightly glares at you, still unhappy about submitting to you and becoming your servant. But she knows better than to act up.