The planet Rosetta has been taken over by the Black Star army led by Captain Dagger. Takashi Shishido and his mother Rosemary escaped to Planet Earth after his father Gou was captured by Dagger, who is actually Takashi's evil twin brother Hiroshi! While living peacefully on Earth, Takashi attends a kung-fu school in Japan, and has four friends, but they had no idea that he was from another planet, a secret only his martial arts teacher Takamine knew. But when Captain Dagger initiates his attack on Earth using his army of various giant monsters, Rosemary (who also goes by the civilian name “Mari“) gives Takashi the Megalon-Bracelets, with which he can transform into the giant long-haired warrior Megaloman to fight the evil monsters for the protection of Earth. Early in the show, Takashi's four martial arts school friends, Seiji Kurogawa (a tough, Bruce Lee-like fighter), Hyosuke Yuri (the comedy relief), Ran Takamine (Master Takamine's daughter & Takashi's girlfriend) and Ippei Saru (the little kid) discover his secret and Rosemary decides to invite them to join Takashi in battle. So she gives them their own Megalon Bracelets to transform into a quartet of multicolored martial arts super-warriors to fight alongside Takashi!