"Kinnikuman Nisei: Muscle Ninjin Sōdatsu! Chōjin Daisensō" is a direct continuation of the "Kinnikuman Nisei" series, focusing on the next generation of characters in the Kinnikuman universe. The story revolves around Mantaro Kinniku, the son of the legendary wrestler Suguru Kinniku (Kinnikuman), as he navigates the challenges of being a Chōjin (superhuman wrestler) while protecting Earth from various threats. The central plot involves the emergence of a powerful artifact known as the Muscle Ninjin, a mystical carrot-shaped object that grants immense power to its wielder. This artifact becomes the target of multiple factions, including the evil Chōjin group known as the DMP (Dangerous Mind Power), who seek to use it for destructive purposes.

Mantaro, alongside his friends and allies, including his loyal partner Meat and the skilled wrestler Checkmate, embarks on a mission to retrieve the Muscle Ninjin before it falls into the wrong hands. The narrative unfolds through a series of intense wrestling battles, combining action, comedy, and elements of science fiction. Mantaro’s journey is marked by personal growth, as he learns to harness his inherited abilities and live up to his father’s legacy. The series also explores themes of friendship, perseverance, and the responsibility that comes with power, as Mantaro and his team face increasingly formidable opponents.

The story introduces a diverse cast of characters, both allies and adversaries, each with unique wrestling techniques and personalities. Notable antagonists include members of the DMP, such as the cunning and ruthless Scarface, who serve as recurring threats throughout the series. The episodic structure of the narrative allows for a mix of standalone battles and overarching plotlines, culminating in high-stakes confrontations that test Mantaro’s resolve and abilities. The series maintains a balance between lighthearted moments and intense action, staying true to the tone of the "Kinnikuman" franchise while expanding its lore and introducing new elements to the Chōjin wrestling world.