K (Shinji Takeda), a young Japanese debugger and freelance programmer (also Techno LPs collector in his free time), is a vigilante who non-fatally shoots wrongdoers as he encounters them in his daily life. Before each shooting, he dons a pair of thick glasses. The local media quickly hones in on the mystery, dubbing the attacker Four-eyes (Le Bigleux in the original version, literally "the poor-sighted").
Hinano (Hinano Yoshikawa) is a seventeen-year-old hairdresser who lives with her older brother Roy (Roy), a police officer assigned to the Four-Eyes case. While riding the subway, she notices a young man secretly filming other passengers and, driven by curiosity, starts to trail him. She eventually asks her friend and coworker Naomi (Naomi) to join the investigation.
Hinano and K strike up a friendship, and he invites her to his apartment, where he opens up about his worlds of trance music and video games. Hinano is wary at first, but curiosity and attraction pull her deeper into his unconventional world, pulling her away from the ordinary life she knows.
Meanwhile, Roy continues to chase leads on Four Eyes, but the case stalls. Hinano witnesses one of K’s shootings and wrestles with what this means for her. She confronts K, who explains that he has modified his pistol to be inaccurate, ostensibly to ensure the bullets miss their targets. Yet the tension escalates when K inadvertently kills a man who is breaking up with one of his girlfriends.
In a later confrontation, K reveals a cruel paradox: he uses the thick glasses to keep his victims still, and he admits that he could not shoot them if he looked them in the eye. He also explains that his videos stem from a broader impulse to observe the world, not merely to act. Despite his vast trove of footage, he concedes that seeing clearly is still a struggle. He tells Hinano that he could renounce Four-Eyes, presenting a possibility of separation from the persona that has haunted him, which gives Hinano a glimmer of reassurance.
A pivotal moment arrives when a low-ranking yakuza member, portrayed by Beat Takeshi, arrives to retrieve K’s handgun. The weapon, left on loan, fires unexpectedly and pierces K’s lower abdomen. Rather than heading to a hospital, K chooses to continue wandering with Hinano, and he asks her to meet him at the top of Tokyo’s tallest building. Hinano stands at the observation deck, waiting, while K, wounded, staggers toward the edge of a busy street. In the final scene, Hinano walks away, only to feel a hand grab hers and look up to find K’s smiling face watching over her.
The ending remains deliberately ambiguous: it is unclear whether K survives. Notably, the international version, as well as the Japanese original, includes about seven minutes of additional footage that may offer a more explicit resolution than the original cut.
