You are Ms. Servant

This is the story of a maid who is all alone in the world, but who finally finds a family. Told from an early age that her only worth is as a killer, Yuki had known nothing else except cold efficiency and following orders. Now that she has a chance to leave her past behind, she arrives at the doorstep of Hitoyoshi Yokoya, asking to be employed… as a maid. Thus begins the journey of a former assassin learning what it means to be ‘normal’. <em class=de-emphasized>(from manga)</em>

Synopsis from Anime News Network