The series opens as planet Rosetta has been taken over by the Black Star army led by Captain Dagger (Yuki Kitazume). Takashi Shishido (also played by Yuki Kitazume) and his mother Rosemary (Yukiko Takabayashi) escape to Planet Earth after his father Gou was captured by Dagger. In a shock revelation, not at all revealed by the fact they are played by the same actor, it turns out Captain Dagger is actually Takashi’s evil twin brother Hiroshi!
While living peacefully on Earth, Takashi attends a kung-fu school in Japan, and makes friends with four of its students- Seiji Kurogawa (Jimmy Araki), Hyosuke Yuri (Pepe Hozumi), Ran Takamine (Madoka Sugi) and Ippei Mashira (Kôji Hashimichi). They have no idea that he was from another planet, this secret is only known by his martial arts teacher Sougen Takamine (Takao Inoue) – Ran’s father. Soon Ran and Takashi begin a relationship but this is interrupted when Captain Dagger initiates his attack on Earth using his army of various giant monsters.
When the atttack begins 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 series the four friends discover Takashi’s secret so Rosemary decides to invite them to join Takashi in battle. She gives them their own Megalon Bracelets to transform into a quartet of multicolored martial arts super-warriors to fight alongside Takashi!