Kimiko Kujo is a character exclusive to the live-action film L: change the WorLd, which serves as a spin-off to the Death Note film series. She also appears in the accompanying novel adaptation. Within the story, Kujo is introduced as a respected viral researcher and a member of Wammy's House, the secretive orphanage for gifted children originally established by Watari to nurture successors to the detective L. She works as an assistant to Dr. Kimihiko Nikaido at the Infectious Disease Centre of Asia, where they jointly handle a deadly artificial virus. Behind this professional facade, she is the secret leader of a bioterrorist organization known as Blue Ship, and she frequently operates under the alias K.

Kujo is driven by a profound misanthropy and an eco-fascist ideology. She believes that humanity's unchecked population growth and pollution are destroying the planet, and she considers the mass elimination of human life through a manufactured pathogen to be a justified means of restoring environmental balance. This worldview makes her ruthless and utterly committed to her cause; she shows no hesitation in sacrificing innocent lives to achieve her goal. Her personality is calm, calculating, and manipulative, allowing her to maintain a convincing double life as a dedicated scientist while orchestrating a global-scale catastrophe.

In the narrative, Kujo's true nature is revealed when Dr. Nikaido creates an antidote to the virus. She confronts him, demanding the formula, but he refuses, destroys the sample, and injects himself with the virus to prevent her from obtaining it. She kills him without remorse, then shifts her attention to his young daughter Maki, convinced the girl possesses the knowledge needed to recreate the antidote. This act sets off a pursuit that forces Maki to seek shelter with L, who is living out his final twenty-three days after writing his own name in the Death Note. Kujo deploys her resources to track the girl, leading to a series of confrontations that culminate in a plan to spread the virus aboard an airplane. She ultimately kills Dr. Nikaido and attempts to leverage Maki's infection to infect others. L intervenes, halting the plane and administering the antidote. When Maki tries to kill Kujo out of revenge, L prevents her, and Kujo is subsequently arrested by authorities.

Kujo's key relationships are defined by her betrayal and her opposition. She was Dr. Nikaido's trusted colleague, yet she murdered him without hesitation. With Maki, she alternates between seeing the girl as a tool to secure the antidote and as an obstacle to be removed. In relation to L, she represents a final challenge for the dying detective, pitting her bioterrorism against his intellect and determination. Kujo does not undergo a personal development arc; she remains unwavering in her extremist beliefs until her capture. The film does not grant her a moment of redemption or self-reflection.

Her notable abilities stem from her scientific expertise in virology, which enables her to create, weaponize, and attempt to spread the engineered virus. She is also a skilled organizer and leader, commanding a network of operatives and directing a complex terror operation from the shadows. Her capacity for deception is equally significant, as she successfully impersonates a benevolent researcher for years while secretly plotting genocide. These traits make her a formidable antagonist in a story otherwise centered on the intellectual and physical vulnerabilities of L.