"Kaijū Sekai Seifuku" centers on a world where humanity coexists with kaijū, giant monsters that have become an integral part of society. The story unfolds in a near-future setting where kaijū are no longer seen as threats but as tools for power and control. The narrative follows a young man named Haruo, who becomes entangled in a conflict between factions vying to dominate the world using kaijū. Haruo, initially an ordinary citizen, discovers a unique ability to communicate with these creatures, setting him apart as a key figure in the struggle for global supremacy.

The plot explores the political and social implications of kaijū integration, with various organizations and governments seeking to harness their power for military, economic, and ideological purposes. Haruo is drawn into a secretive group known as the Kaijū Liberation Front, which aims to free kaijū from human exploitation and establish a new world order. As the story progresses, alliances shift, and Haruo must navigate a complex web of betrayals, moral dilemmas, and escalating conflicts.

Key characters include Haruo, whose empathy for kaijū drives his actions; Akira, a skilled kaijū pilot and Haruo's childhood friend, who represents the military-industrial complex; and Rika, a scientist dedicated to understanding kaijū biology and behavior. The series delves into themes of coexistence, power dynamics, and the ethical treatment of sentient beings, all while maintaining a focus on the high-stakes battles and strategic maneuvering between human factions and kaijū. The narrative builds toward a climactic confrontation that challenges the very foundations of the world order, leaving the fate of humanity and kaijū intertwined in uncertain ways.