Shizune Orikasa, a graduate student studying physics, witnesses the occurrence of neutrino data that could easily be mistaken for a supernova, which is normally impossible. In the next moment, a beautifully young girl, almost naked, appears before him. She introduces herself as Aria, a mechanical slave who has come from another world in search of a new master. Shizune chooses to become her master, but in this world, there are other mechanical slaves and their owners existing as well――.