A long time ago humanity went extinct thanks to some invading monsters. The rest of the sentient beings in the world survived by escaping to floating islands. Though sheer luck a human named Willem is resurrected from a petrifaction curse and finds himself as the last human alive. He accepts an odd job offer one day where he is to watch over some weapons. In an obnoxious twist of fate these weapons are a group of girls left over from the leprechauns. These girls secretly fight on behalf of the inhabitants of earth. Now all Willem can do is hope that these girls come home after each of their missions.