Planet Earth is on the brink of invasion after humanity ruined the peace and quiet of the universe with the broadcast of metal music on the Voyager probe's Golden Record. Aliens picked up the signal and couldn't stop headbanging, and now they're dying off because of it… so they want revenge!

A few rogue extraterrestrials make their way to the source of the music and abduct two high school students from the Tokyo suburb of Kichijoji: an unnamed boy, and a drummer named Rinko from an outrageous girls-only metal club. The aliens needed an emissary with whom to discuss the terms of their revenge, and felt either of these two would serve nicely. However, being unable to choose between them, the aliens simply decided to merge their souls into a single being!

Now, working together, the all-in-one pair must team up with the other members of K.M.G. (the Kichijoji Metal Girls) to rid the planet of these eight-tentacled extraterrestrials using the power of metal. It’s time to rock these music-hating creeps all the way back to whatever planet they came from!