No one is entirely sure where the man named Bruno Kaiser came from. Somewhere from the slums of Germany. Either way, that wasn't important. What was important about this man named Bruno was that he was possibly the most arrogant man alive, and was a blood supremacist. Top that off with a pinch of absolute ruthlessness, and you've got a recipe for disaster.
Bruno was supremely intelligent and physically capable. He firmly believed that he akin to a god punishing the unworthy, and he went around torturing half-bloods, muggle-borns, muggles... anyone that wasn't pure-blood really. Ninety-nine percent of the time, Bruno's torture was too much for his victims and they died.
At some point Bruno met some other people, that developed into an alliance of sorts. One of those people in the alliance was Rosine's mother named Adeline Faust. Now the two of them were not in love, but things happen, and things happen a lot faster when you're drunk. The end result was that Adeline became pregnant. Use your imagination as to what happened. Either way nine months later Adeline was dead and Rosine Kaiser was born. Adeline died in childbirth.
Eventually Bruno's alliance disintegrated because everyone seemed to have different goals in mind. Bruno taught his daughter every thing he knew and exposed Rosine to the torture from a young age. However he told her not to enjoy it, but to do it because it was out necessity. The world needed to be cleansed of the unworthy, and it was Bruno and Rosine's job to do it. Now Bruno always had an obsession with creating the perfect body of fitness, and he was extremely skilled with potions. Naturally, the solution was to make a potion that would enhance Bruno's physiology. It took many, many year but he eventually succeeded. He didn't write down the recipe for fear that his mortal enemy, the protector of the unworthy, would get his hands on it. Unfortunately, Bruno got drunk that night and forgot the recipe.
During Rosine's first year, the members of Bruno's former alliance got together to one more heist. They left the kids at one person's house and they all just kind of became close friends. When they went off to Hogwarts, they stayed close friends knowing that their is strength in numbers. Even Rosine grudgingly admits to that.
Rosie's life goal is to replicate her father's potion and to remember the dam*ed thing. Since that serum is insanely difficult to make she settles for intense training. It's worked great, Rosine is an excellent hand to hand combatant and an even better marksmen with any gun. She's no slouch with combat magic either. When Rosine arrived at Hogwarts she got sorted into _______ house, and is currently a fifth year.