Hitoyoshi Yokoya is a high school student who currently lives alone. One day, an unfamiliar girl knocks on his door and offers to be his maid. She reveals that she is a former assassin, which makes Hitoyoshi nervous. But when her skills save him from being run over by a truck, Hitoyoshi ultimately decides to take her in. However, the mysterious girl actually has no household skills. In fact, her only expertise is assassination, as she has lived her entire life for the sake of killing. Nonetheless, her time with Hitoyoshi allows her to experience new emotions she had never felt before, inspiring her to become a regular girl. In order to advance toward this upcoming chapter in her life, she asks Hitoyoshi to grant her a new name, to which he names her Yuki. Having someone she can finally consider family, Yuki acquires new fond memories that fill her heart with warmth as she tries to leave her dark and lonely past behind.