In a world where humans and demons coexist, Demon Lord Tasogare holds the human empire's princess, Aurora Suya Rhys Kaymin, hostage. He demands humans to give him absolute rule on the world, but humanity refuses to concede without a fight and sends Yuusha Akatsuki to save the captive.

Meanwhile, although unharmed, Suya Rhys spends her time locked up in the demon castle, often feeling lethargic. Even so, she has trouble sleeping due to poor hospitality. The princess then begins her amusing adventures as she tries to make herself comfortable and finally get some sleep.