Rei is a special agent for Section Zero, a covert police network so secret that it operates in the shadows of modern Japan, invisible to the average citizen. Her undercover identity is so well-guarded that no official records of her exist. Known for her lethal efficiency and a willingness to use any means to complete an assignment, Rei is dispatched to investigate Hideo Kayama, a mysterious criminal suspected of purchasing and reselling guns and drugs that were originally confiscated by corrupt police officers.

As Rei infiltrates Kayama's organization, she discovers he is a man without a past, a ghost who, like her, appears in no government records or official documents. This parallel existence creates a dangerous attraction between the agent and her target. Rei gains Kayama's confidence by working as a courier and assisting him in eliminating a business rival, but she soon finds her professional resolve compromised by her growing personal feelings for him. Her superiors in Section Zero become concerned that she is losing focus on her mission. Complicating matters further, Rei must also navigate threats from Kayama's violently jealous lover. Set against a backdrop of corporate crime and institutional corruption, the story follows two invisible people drawn together, exploring what happens when two zeros meet in a world where neither officially exists.