In 1980s, an evil alien race known simply as the Invaders are about to take over the Earth, using assorted daikaiju (giant monsters) and other fiendish plots. Assigned to investigate this threat is an organization called the Science Guard Members (SGM). But another hope comes from someone, unbeknownst even to himself, possessing otherworldly power. Professor Mitarai, the leader of SGM, finally shares a secret with his foster son, young photojournalist named Kyôtarô Kagami ("kagami" = Japanese for "mirror"), a secret only he himself knows: Kyôtarô a half-cast of an alien father and a human mother (both of whom are missing — captives of the Invaders). Kyôtarô discovers that he is actually the son of Mirrorman, a superhero from the 2nd Dimension. However, the original Mirrorman was defeated by the Invaders' toughest monster King Zyger (explained in Episode 14), but his son Kyôtarô survived, and shares the same powers as his namesake. Naturally, the young man had difficulty accepting his destiny, but he soon realizes that he is the only one who can save the Earth from the Invaders, when they try to assassinate him. In order to transform into Mirrorman, Kyôtarô must stand in front of any reflective surface (mirrors, water, etc.), and flash his Mirror-Pendant, and utter the words "Mirror Spark".