Vesper is a covert organisation that uses super-powered war androids to fight an army of extraterrestrial invaders. Mahoro is Vesper's most powerful fighting android, and she has won several battles, but she has a limited operational period and will soon cease to operate. However, if she lays down her arms and conserves her remaining power, she may extend the time she has left to slightly over a year. Mahoro is offered the option to live the rest of her life as a regular human. She chooses to work as a maid for Suguru, a spectacularly dirty high school student who lives alone after his family died.