An ordinary social worker, Natsukawa Hoshino, suddenly inherited a dilapidated apartment left by his missing grandfather. He soon discovered that the tenants of this apartment were not human beings, but a group of the last orphans from different destroyed civilizations. As the new "administrator", he not only has to deal with the trivial matters of his alien neighbors and hide their secrets, but he also has to face a huge conspiracy behind the "Galactic Civilization Trusteeship Agreement" and uncover the truth about his grandfather's disappearance.
