The Cranassians are the villainous force from the Raiden series. These are alien invaders who want to conquer our world, starting an invasion in the year 2090. The World Alliance Military captures one of their vessels, and based on it they create the Raiden series of fighters, in order to counter the Cranassian invasion. The World Alliance Military has been successful in their fight against the Cranassians, having defeated them four consecutive times, though the Cranassians don't show signs of ever giving up.
The Cranassians headquarters is located on a large space station, surrounded by an asteroid belt. Their forces are comprised of various military machines and aircraft, all of which are controlled by a red crystal(called Energen Crystal) which also serves as a power source. The crystals themselves are apparently sentient, since whenever their vessels are destroyed, the crystal will leave the machine and fly away.