"Kinnikuman: Seigi Chōjin vs Kodai Chōjin" is a continuation of the "Kinnikuman" series, focusing on the conflict between the Seigi Chōjin (Justice Supermen) and the Kodai Chōjin (Ancient Supermen). The narrative centers on Suguru Kinniku, also known as Kinnikuman, a clumsy yet determined wrestler who is revealed to be the prince of Planet Kinniku. The series delves into the origins of the Chōjin race, revealing that the Kodai Chōjin, the original supermen, were sealed away long ago due to their destructive nature. They have now returned, seeking to reclaim their dominance over the universe.

The Kodai Chōjin, led by the powerful and ruthless Akuma Shogun, challenge the Seigi Chōjin to a series of high-stakes wrestling matches. These battles are not merely for sport but for the survival of humanity and the balance of power in the universe. Kinnikuman, alongside his allies such as Terryman, Robin Mask, and Ramenman, must confront these ancient adversaries, each of whom possesses unique and devastating abilities. The matches are intense and often push the Seigi Chōjin to their limits, requiring them to dig deep into their reserves of strength, strategy, and camaraderie.

Throughout the series, the backstory of the Kodai Chōjin is explored, revealing their motivations and the reasons for their imprisonment. The narrative also delves into the personal growth of Kinnikuman and his friends as they face increasingly formidable opponents. Themes of redemption, loyalty, and the struggle between good and evil are prevalent, as the Seigi Chōjin fight not only for victory but to prove the worth of their ideals.

The series is structured around a series of episodic battles, each highlighting different characters and their unique wrestling techniques. The stakes escalate as the Kodai Chōjin grow more desperate and their plans more sinister, culminating in a final confrontation that tests the resolve and unity of the Seigi Chōjin. The story balances action with moments of humor and character development, maintaining a dynamic pace that keeps the audience engaged.

"Kinnikuman: Seigi Chōjin vs Kodai Chōjin" builds on the established lore of the "Kinnikuman" universe while introducing new elements that expand the narrative scope. It remains true to the series' roots in wrestling and heroism, delivering a story that is both entertaining and thematically rich. The characters, both old and new, are given depth, and their interactions drive the plot forward, making it a compelling continuation of the "Kinnikuman" saga.