Out on a routine mission, Nanairo Planetary Patrol Officers Rallen and Jeena respond to a strange distress signal and discover the wreckage of an escape capsule in which an old man has been in a cryogenic sleep for over a decade. Once conscious, the man, whose name is Aldous, relays an unbelievable tale of the attack on his home planet by a vicious horde of creatures known as the Krawl. Rallen, Jeena, and Aldous then set out on a mission to save Nanairo from the destructive planet-eating Krawl.
After fighting the Krawl on five of Nanairo's seven planets, Rallen's boss, Commander Grant, reveals that the Krawl had established a base on the seventh planet, Meido; however, their spaceship is incapable of reaching this planet. Aldous reveals that ancient ruins found on one of the planets are actually a spaceship from an earlier civilization, and that it may be able to reach Meido. After gathering a number of Keystones, they are able to resurrect the spaceship and reach the Meido. After fighting through more hordes of Krawl, Rallen fights a large Krawl called Xelles that has the ability to heal whatever comes near it. After defeating it, Rallen fights a final Leader Krawl and kills it, thus ending the invasion - temporarily.