The World Government intended that the fact-finding mission to Galaxy X1X be kept under wraps; yet information gathered from the mission had later leaked to the press and confirmed the public's most dreaded suspicions; extra-terrestrial mutants from the BYDO Empire were indeed consolidating their forces and soon would be departing their space bases to launch an all-out attack on the Earth. It's up to you now in your R-TYPE Spaceship to stop this threat.

--From the Gameboy/Gameboy Color R-Type DX instruction manual.