As the whole world watches the Choujin Rugby game on TV, the "Underground Space Emperor" Hydra King has his Underground Space Supermen kidnap Robin Mask. Their aim is to lure out the Seigi Choujins and then attack them using the Robin Memo, which contains info on all of the Seigi Choujin's weaknesses. Watching on TV all over the world, Kinnikuman and the Seigi Choujins get together and head for Planet Hydra. (Source: Kinnikuman Wiki)

Counterattack! The Underground Space Choujin is the fourth theatrical film based on the anime series Kinnikuman. It was released in Japan on July 13, 1985 alongside Dr. Slump and Arale-chan: Hoyoyo! Dream Capital Mecha Police, Captain Tsubasa: Great Europe Play-Off, and Dengeki Sentai Changeman: Shuttle Base Showdown. It is set after the Golden Mask Arc. It is the first film to feature the character Geronimo and the last film where Eiji Kanie supplies the voice of Ramenman. It is also the shortest film of the series. It is based on theKinnikuman special chapter Robin Memo (ロビン･メモ). (Source: Kinnikuman Wiki)