"Godzilla: City on the Edge of Battle" is the second installment in the Godzilla anime trilogy, continuing the story from "Godzilla: Planet of the Monsters." The narrative picks up after humanity's failed attempt to defeat Godzilla on Earth, with the surviving members of the Aratrum crew regrouping on a nearby planet. Haruo Sakaki, the protagonist, remains determined to destroy Godzilla and reclaim Earth for humanity. Alongside him are key characters such as Metphies, a mysterious Exif priest, and Yuko Tani, a skilled pilot and Haruo's close ally.

The story shifts focus to the discovery of Mechagodzilla, an ancient anti-Godzilla weapon buried beneath the Earth's surface. This massive machine, referred to as "Mechagodzilla City," was created by an advanced civilization known as the Bilusaludo, who once inhabited Earth. The Bilusaludo survivors, led by their engineer Mulu-elu Galu-gu, propose using nanotechnology to reactivate and control Mechagodzilla, integrating it with their own technology to create a formidable weapon against Godzilla. Haruo reluctantly agrees to this plan, despite his distrust of the Bilusaludo's methods and their willingness to sacrifice individuality for collective efficiency.

As the team works to revive Mechagodzilla, tensions rise between Haruo and the Bilusaludo, particularly over the ethical implications of their nanotechnology, which threatens to assimilate human consciousness into a hive mind. Meanwhile, Metphies continues to manipulate events, subtly pushing Haruo toward a darker path. The narrative explores themes of humanity's resilience, the cost of survival, and the moral dilemmas of using advanced technology.

The climax centers on a final confrontation with Godzilla, who awakens and attacks Mechagodzilla City. The battle reveals the limitations of the Bilusaludo's technology, as Godzilla's overwhelming power and regenerative abilities prove nearly insurmountable. Haruo is forced to confront the consequences of his obsession with defeating Godzilla, as the conflict pushes him to the brink of losing his humanity. The film ends on a cliffhanger, setting the stage for the trilogy's conclusion, with humanity's fate still hanging in the balance and Haruo's resolve tested like never before.