During United Earth Year 192, the Earth is under attack from an extraterrestrial enemy known as the Radam; parasites that take humans as hosts. The Radam forces comprise of grotesque bug-like monsters that are led by armored soldiers known as the Tekkamen. Surrounding the Earth is an enormous man-made ring-shaped structure known as the Orbital Ring System. The Orbital Ring was a space station that once served as a launch point into space and was constructed well before the arrival of the alien invaders. It was thus the first human structure attacked and occupied by Radam, with its human inhabitants having either fled or been killed. Now it serves merely as a battle ground for the military against the aliens.
Fighting against the Radam and their Tekkamen are the Space Knights. Led by Commander Heinrich von Freeman, the Space Knights are a special defense force and Earth's last hope for defeating the Radam. The Space Knights consist of Noal, the pilot of the Space Knights' ship "Blue Earth"; Aki, the Blue Earth navigator; Milly, the communications operator; Levin, computer mechanic; and Honda, mechanic and repairs. The Space Knights have been unsuccessful at repelling the aliens until the arrival of D-Boy, a young man who has the ability to transform into an armored warrior known as Tekkaman Blade.