A girl called Zero stands in a crowded street, her occupation an assassin. As she completes her tasks one after another, Zero has been feeling uneasy lately. As her code name suggests, she has nothing to prove her existence. She overlaps herself with the vanishing landscape and begins to wander in search of the meaning of her own existence. At the same time, a young man named One is also wandering the streets, and like Zero, he is an assassin. Surrounded by a sense of emptiness, he is unable to find the value of his own existence. One day, the two of them meet as if they were led together. They sense each other, and by touching each other, they regain their existence and humanity. However, the organization feels that contact between assassins is dangerous, and decides to dispose of them. They call in a highly skilled assassin. Their battle for their own existence begins now!