The Iridion is the villainous force from the Iridion series.
Iridion is an alien force from the far reaches of the galaxy, which without warning invades Earth and successfully takes over, leaving its forces positioned on the ocean and atmosphere. A pilot of the experimental SHN fighter, which was testing the ship, returns to Earth only to find the planet taken over by the Iridion forces, so he decides to fight against them. He defeats the invading forces, reaching into the sky and the planet's orbit, and following them to the moon.
With the invasion crushed, the SHN proceeds to follow the Iridion forces and take the battle to their own home planet (7th stage), Planet Iridion Prime, where he destroys the Mainframe which had been controlling the Iridion forces (8th stage; although labelled as stage 7 it is actually 8). With its destruction after a vicious and grueling duel, the remaining forces disappeared and the alien threat ended.
Or so it seemed...
A century passed since the Iridion invasion, and humanity began to colonize the planet systems on the Iridion galaxy. Peace is disturbed again, however, as the Iridion force returns, rearmed, rebuilt and furious, and starts violently reclaiming planets which had been its. Since Earth was too distant to send help in time, a new pilot in new age is assigned to the SHN fighter called SHN-27 and sent to fight back the Iridion forces by himself.
Iridion forces occupy five galaxies naming Alpha, Beta, Delta, Gamma and Epsilon Galaxies: each galaxies consists three planets each, and after three planets are cleansed of Iridions, clearing one galaxy, then SHN-27 moves to the next galaxy to fight Iridion military (consisting 15 stages in total). SHN-27 successfully liberates the planets taken over by the Iridion, following them into their new headquarters, where the mighty fighter destroys the new Iridion mainframe called Mainframe 2.0 along with the planet where Mainframe 2.0 resided, once again putting an end to Iridion's schemes (and once again obliterated by a single human pilot).