I rewrote my idea so it has 3 plot options now~ (MxF, looking for F)

Your character lived a peaceful and happy life. Enough food on her plate, a loving family, occasionally watching the knights train (or even join them), an almost boring but good life. But it came to an abrupt end when bandits raided her town. Flames everywhere, buildings collapsed, the streets turned red with blood. And in this whole chaos, your character. Because she looked good however, she was not killed like most of the townsfolk. Just mildly injured at best, so that she later could be sold as slave. 

Some time passed, and eventually, she finds herself in the back of an auction house. This was it. The end. Someone was about to buy her, and from there on out, only the worst of the worst could happen. It was unfair! She didn't deserve this! She was just a common citizen, thrown in here by bandits. Thinking about the night over and over, her sadness slowly changed into something else. A deep burning need. Justice? Revenge? Whatever it justification it was, even if there was no hance she could have it, her very soul cried craved but one thing. Death to those bandits.

People looked at her, made comments, and left when the guards announced that the auction was about to start. Except for one presence. Suddenly, there is a voice behind her. "Sup?" The person behind her was... unsettling. Odd eyes, black sclera, short white hair, and a white coat. Waiting till her reaction passed, he would then ask "Yes yes, I know. But no. Not a demon. But tell me. Why do I feel like you, unlike most others here, want to kill someone really badly?"

And from that point we continue.

You are absolutely welcome to change details about this to your liking. Maybe have a specific person who did this to her, betrayal, or specific details about her time as a slave. The only details I would like to keep is that there is a slave who really, absolutely wants someone to be very dead, and for my character to provide her with such an opportunity. 

My character would be looking for a slave to assist him in his work, but having a slave spellbound with magic tools, or just regular beatings is not something he is interested in. It could be much easier. A fair deal. He'd help her get her revenge, train her, teach her magic, let her earn her own money even, if she in return simply did as she was told when he needed her.

Your character comes from the modern world. A fan of games and shows perhaps, has probably seen or at least heard of the concept of an isekai herself. And one day, it happened. A spell was cast right under her, and before she knew it, she stood in a big hall, surrounded by mages, and welcomed by a king. She was summoned to be a hero, to bring prosperity and get fame and fortune in return. But first things first. Surely she wanted to adjust herself to this world first, and was given a room and good food until preparations were done. 

On the same night however, there was suddenly unrest in the castle, and she could hear fighting from the other side of the door of her room. The sound of armored knights falling, weapons against the hard stone floor. And steps. Steps that came closer and closer until... *knock* *knock*. (At this point either she opens it, or the invader does, which is up to you). Once the door is open, the man in front of her wastes no time and talks before she can. "So... Unless you want to get exploited by nobility, how about I bring you out of here?" He would quickly go on to explain that summoning was a forbidden art, since humans summoned this way tend to have incredible powers. A nation supported by such a hero could easily tip the balance of the world in their favor. This is something my character is not willing to let happen. 

I also have a suggestion in mind for which power for your character to have, but I know you have your own ideas too, so by all means. Bring your idea. And if you don't have one or are curious, ask me.

Your character has become sick a long time ago, and has for quite some time just learned to deal with it and get by. But recently, it got worse. Word is send out that a doctor is needed, and those who come are either not sure what is wrong, or attempt to sell really expensive medicine. Those who try the latter don't even suggest the same things. But then, my character would hear of this call for medical help, and examines her differently. Asking more questions, listening to her body by putting his ear on her back. 

It would turn out that she has a bacterial infection. One that would slowly kill her. As he explains the treatment, she asks for the price. It is more affordable than what the other doctor's asked for, but still a bit out of her family's budged. So as their hearts sink, he suggests that she can come work for him, help him make medicine like this and others as soon as she is back to full health.