You are Ms. Servant.

Living alone, high school student Hitoyoshi Yokoya is approached by a stranger who offers to be his maid, with one caveat; she’s a former assassin. Hitoyoshi is understandably unnerved, but after she saves him from a truck, her combat know-how impresses him enough to give her a chance. However, it quickly becomes clear that Yuki, as he christens her, has no home-making skills, only expertise in assassination, which she has honed for years. Spending more time together, Yuki begins to develop new emotions, and desires a life free from violence. Renaming herself, she begins a new life thanks to her new family with Hitoyoshi, leaving behind her haunted past.