Yokoya Hitoyoshi is a young high school student living alone, as his family is away from home almost constantly. The boy lacks the motivation to keep his place clean and often suffers from loneliness. One day, a beautiful maid appears at his gate and asks to be hired. As they talk, she eventually reveals that she has worked as a professional assassin since she was a child. However, her employer has retired and recommended she go to the Yokoya estate, which supposedly belonged to his distant relatives.
