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.In the past evil superhumans invaded earth to conquer the human race. A group of superhuman calling themselves the muscle league challenge the evil. One of the muscle league member, King Muscle displayed great strength and skill. With his help the muscle league defeated the evil and once again peace retuned to earth. 28 years later a new evil force has come to conquer the human race, but legendary heros who fought in the past were too weak and old to beat the new threat. Now they trained a new league of warriors to fight.