Misa Amane receives a Death Note from Rem, another Shinigami, setting the stage for a tense new arc. As Light Yagami joins the task force after Shiori's funeral, Misa ascends to the role of the Second Kira and pushes a TV station to broadcast her taped messages, turning the case into a public spectacle.
With her Shinigami Eyes, Misa eyes the world through the screen and uses her power to strike at a prominent Kira critic, then targets Detective Mogi and two officers who were trying to disperse a rally in support of Kira. The violence shakes the investigation and raises the stakes for everyone involved. Light’s younger sister, Sayu Yagami, is nearly killed in the chaos, but Soichiro Yagami (Soichiro Yagami) crashes into the festival on a motorcycle helmet, masking the attacker from sight and saving Sayu’s life.
Light arrives to comfort Sayu and Soichiro, though Misa catches sight of him and pieces together that he is Kira. Misa seeks to ally with Light, hoping to join his mission to “cleanse” the world, and Light, recognizing her Shinigami Eyes, agrees to work with her. He arranges a meeting between Misa and L, hoping to uncover L’s true name and throw the investigation off balance. But Misa is soon arrested by L’s team, tied to the evidence surrounding the taped messages.
Fearing a confession, Light hatches a bold plan: he and Misa will forfeit their Death Notes, effectively erasing their memory of the events. Light buries his own Death Note, while Rem transfers the other Death Note to Kiyomi Takada, a reporter covering the Kira case, inflaming the political intrigue surrounding the mystery. The strategy is meant to buy time and sow doubt about Kira’s true identity, all while Light positions himself to be seen as innocent.
After a period of surveillance, Light and Misa are released, but kept under constant watch by L. Light stumbles upon a clue pointing to Takada and helps the police arrest her, shifting the investigation and revealing to the authorities the existence of Death Notes and Shinigami. In a gamble to restore his memories, Light uses a fragment of a Death Note hidden in his watch to kill Takada, exposing a crucial loophole that makes the public believe he is innocent after all.
Earlier, Light had embedded a supposed rule into the Death Note: once a name is written, the name must be written again every thirteen days or the person will perish. The police, convinced the rule is genuine, accept that Light and Misa were unjustly detained and exonerated. With renewed confidence, Light convinces Misa to locate the buried Death Note to target L. Misa, however, had forgotten L’s name, and she resumes Kira’s killings in the meantime.
L adapts his strategy by sending the main task force, leaving only himself and Light in place, to test the authenticity of the thirteen-day rule by staying in one location. Suspicion soon falls on Misa, and Rem is forced to take drastic action: she kills Watari and L to protect Misa from another arrest. The Shinigami rule forbidding protection of humans means Rem’s death is a heavy price for stepping into the fray.
To end the investigation, Light writes his own father’s name in the Death Note, hoping to demonstrate his innocence; however, his father survives, leaving Light cornered by the police. L then reveals a staggering twist: he had written his own name in the Death Note, scheduling his death in advance and thereby becoming immune to further writings. He also discloses that the Death Note Light used was a decoy and that the task force never left for America; they had been surveilling Light from a hidden vantage, watching him reveal his true identity as Kira.
Desperation peaks as Light pleads with Ryuk, the Shinigami, to kill the surrounding officers, but Ryuk chooses to take Light’s life instead. Ryuk explains the cosmic consequence for owning a Death Note: a human will be denied Heaven and Hell and spend eternity as nothingness. Light dies in his father’s arms, begging his father to believe that his actions were an attempt at justice.
In the wake of Light’s death, the police decide to cover up the truth and declare that Kira killed Light and then killed himself. Twenty days later, Soichiro meets L one last time before L dies peacefully, leaving the world with a chilling sense of unfinished justice. A year passes, and on Light’s birthday, Soichiro maintains the false narrative for his wife and Sayu, who remain unaware of the Death Note’s true power. Misa also marks Light’s birthday with a quiet affection, but she has no memory of the Death Note or the events that connected them.
The film closes with Ryuk circling Tokyo Tower, laughing at the human drama that unfolded, a reminder of the price of wielding a weapon that can rewrite life and death.
