Mantaro has made it to the semifinal match of the Chojin Cup. He must now fight Ricardo in a soccer field to advance to the last match. Kevin Mask is also in the semifinals, and must defeat Ilioukhine in an aerial field to advance. These three matches will determine who wins the Chojin Cup.

The Chojin Crown, the tournament which Mantaro (Kid Muscle) reluctantly participates in. After going along with the obstacles (most of which were created to try and eliminate him), he qualified.

Kinnikuman II Sei takes place several years after the events of the original Kinnikuman. Mantarou Kinniku is the 59th prince of Planet Kinniku and son of the renowned wrestler, King Suguru. Lazy, immature, and cowardly, Mantarou seems to have little in common with his heroic father. When a powerful group calling themselves the dMP threatens the Earth, only someone as powerful as Kinnikuman stands a chance against them. Not knowing the current whereabouts of the King, a plan is formed to have his son Mantarou take up the mantle. The idea of fighting super villains does not sit well with Mantarou, who initially runs away from his duty. He flees to Earth where he encounters Meat, his father’s old trainer. Despite Mantarou's shortcomings, Meat sees King Suguru in him, and believes he can set the prince on the right path. Thus begins Mantarou's journey to better himself and save the world.

High school student Rakurou Hizutome has a peculiar hobby of playing poorly made games—ones that are unbalanced or are filled with so many bugs that make them borderline unplayable. The few who share his hobby might recognize him by his in-game name, Sunraku. For his next game, Rakurou is recommended Shangri-La Frontier, a popular and well-received virtual reality game as a breather from the terrible games he has been playing recently. Once he boots up the game, Rakurou decides to sell off most of his starting gear to gain extra money, leaving himself with only a pair of boxers, a bird mask, and some weapons. He is instantly hooked as he meticulously levels up his avatar. However, after encountering some intimidating monsters, he realizes that he may have underestimated the challenge that a mainstream game can offer. As Rakurou progresses, he must draw on all the skills he has perfected from his previous gaming experience. Before long, Sunraku's eccentric playstyle takes Shangri-La Frontier by storm.