"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, which they had abandoned 20,000 years prior. The surviving human forces, led by Captain Haruo Sakaki, regroup and discover a mysterious settlement called Mechagodzilla City, built by the remnants of the Bilusaludo, an alien race that once allied with humanity. This city is powered by nanotechnology and is designed to combat Godzilla using advanced technology.

The Bilusaludo, led by their leader Mulu-elu Galu-gu, propose a plan to use Mechagodzilla City's nanometal technology to create a weapon capable of defeating Godzilla. However, the plan involves merging human consciousness with the nanometal, raising ethical concerns among the human survivors. Haruo, driven by his deep-seated hatred for Godzilla, initially supports the plan, but tensions rise as the Bilusaludo's true intentions become unclear. The Bilusaludo prioritize the destruction of Godzilla at any cost, even if it means sacrificing humanity's autonomy.

As the humans and Bilusaludo prepare for the final battle, Godzilla Earth, a colossal and nearly invincible version of the creature, awakens and advances toward Mechagodzilla City. The conflict escalates when the Bilusaludo attempt to forcibly assimilate the humans into the nanometal network, leading to a betrayal and internal strife. Haruo, along with his allies, including the Exif priest Metphies and the Houtua twins, Miana and Maina, must navigate the chaos and decide whether to trust the Bilusaludo's technology or find another way to confront Godzilla.

The climax of the film centers on a desperate battle between Godzilla Earth and the remnants of Mechagodzilla City. Despite the advanced technology, Godzilla proves overwhelmingly powerful, forcing the humans to retreat and reconsider their strategy. The story ends on a cliffhanger, setting the stage for the final installment in the trilogy. Themes of survival, the ethics of technology, and humanity's relationship with nature are explored throughout the narrative, with Haruo's personal vendetta against Godzilla serving as a driving force for the plot. The film maintains a focus on the moral dilemmas faced by the characters as they struggle to reclaim their home planet from the seemingly unstoppable kaiju.