"Kinnikuman Nisei - Second Generations" is a sequel to the original "Kinnikuman" series, set several years after the events of its predecessor. The story centers on Mantaro Kinniku, the son of the legendary wrestler Suguru Kinniku (Kinnikuman). Mantaro is a carefree and somewhat lazy teenager who initially shows little interest in following in his father's footsteps as a Chojin (superhuman) wrestler. However, when the Earth is threatened by a new wave of evil Chojin, Mantaro is reluctantly thrust into the role of Earth's protector.

The narrative begins with Mantaro being summoned to Planet Kinniku, the homeworld of the Kinniku family, where he is informed of his destiny to defend Earth. Despite his initial reluctance, Mantaro undergoes rigorous training to unlock his latent Chojin abilities. Along the way, he forms a team of allies, including his childhood friend Meat, who serves as his loyal sidekick, and a group of fellow Chojin wrestlers who join him in the fight against evil.

The series is structured around a series of wrestling matches, each pitting Mantaro and his allies against increasingly powerful adversaries. These matches are not merely physical contests but also battles of strategy, willpower, and the embodiment of justice. The antagonists, known as the "Perfect Chojin," are a group of elite warriors who seek to dominate the universe. Each member of this group possesses unique abilities and poses a significant threat to Mantaro and his team.

As the story progresses, Mantaro's character evolves from a reluctant hero to a determined and capable leader. His growth is marked by his increasing mastery of his Chojin powers and his deepening sense of responsibility toward his friends and the Earth. The series also explores themes of legacy, as Mantaro struggles to live up to the reputation of his father while carving out his own identity as a hero.

The supporting cast includes a mix of returning characters from the original series and new additions. Notable among them is Kid Muscle, Mantaro's alter ego in the ring, and Terry the Kid, a skilled wrestler who becomes one of Mantaro's closest allies. The series also features a range of colorful and eccentric characters, both allies and enemies, each contributing to the dynamic and often humorous tone of the narrative.

"Kinnikuman Nisei - Second Generations" combines action, comedy, and drama, with a strong emphasis on the camaraderie and rivalry inherent in the world of Chojin wrestling. The series maintains a balance between intense battles and lighthearted moments, making it accessible to a wide audience. Through its engaging storyline and memorable characters, the series continues the legacy of the "Kinnikuman" franchise while introducing new elements that appeal to both longtime fans and newcomers.