After winning the 21st Choujin Olympics, Kinnikuman plans to build his own theme park. As his friends and celebrities arrive, the sky grows dark and with a flash of lightning Kinnikuman's championship belt is gone. He then sees that it has been taken by Octopus Dragon III, who challenges him to take it back. Kinnikuman tries but fails and Mari is kidnapped. Octopus Dragon gives Kinnikuman a time limit to save her before she is fed to the monster Gigasaurus and then returns to his home world of Planet Metro (メトロ星, Metoro-sei?). Despite his injuries, Kinnikuman is determined to go and reclaim his belt and Mari. Luckily, Terryman, Ramenman, Robin Mask, Warsman, Brocken Jr., and Rikishiman arrive to lend him a hand.
Upon arrival on Planet Metro, they are spotted by two minions of Octopus Dragon (series creators Yudetamago in a cameo). They report back to Octopus Dragon, who sends his Kyou'aku Choujin (凶悪超人, Villainous Supermen?) off to stop the Idol Choujins from advancing. They first come across Harigorasu, who is guarding a log bridge. Rikishiman volunteers to fight him and eventually causes them both to fall over into the valley below. Although Rikishiman manages to grab hold of the wall of the valley, he tells Kinnikuman and the others to go on without him as it would take too much time to save him. When Kinnikuman refuses, he lets go of the wall and falls into the valley.
They next meet the ninjutsu Choujin Ukon and his minions. After a comical scene where Kinnikuman mishears Ukon's name as unko (うんこ, poop?), Ramenman and Brocken Jr. volunteer to take them on while the others continue on the journey. As they continue, Robin Mask and Warsman volunteer to take on AmeRug Boss and his minons so Kinnikuman and Terryman can continue. However, Warsman meets up with them again and tells of how Robin threw himself and several of the enemies into an erupting volcano. Warsman then ends up taking on another group of enemies by himself, urging Kinnik
