High school student Hitoto Yokoya finds his life unexpectedly disrupted when a mysterious visitor appears at his home. The guest, a poised young woman with striking black hair, introduces herself as a maid seeking employment. However, her past profession as an assassin and her lack of experience in household chores reveal a stark contrast to her current aspirations. Despite being clumsy and unfamiliar with domestic tasks, she is determined to adapt to her new role. Thus begins an unconventional cohabitation under one roof, marked by curiosity and gradual understanding. Over time, the maid, who initially seemed detached and emotionally reserved, begins to experience subtle shifts in her feelings, hinting at an evolving inner world shaped by this unique connection.