Morinaga Satsuki is the only daughter of a family that owns an antique store, with no special redeeming features she is an extremely normal 2nd year high school student. It's the 24th of August, with one week left in her summer vacation. On the day that her parents leave for a business trip she spontaneously finds a sparkling yellow ring, the "Chrysoberyl".
When Satsuki took that ring and put it on, the man sealed inside was summoned into this world. He called himself a demon called "Ruen Egrandin". He semi-forcefully asked her to help him find the "Thing he was looking for", and as a reward he would grant her a "wish that wasn't particularly a wish".
The thing the demon was looking for was the demon stone "Heliotrope" which was set in another ring.
"That is a ring of destruction. Right after you put it on, no matter how much you struggle, you will easily lose your mind and go insane." It's that kind of frightening ring. However as long as you don't put it on, nothing bad will happen.
Under pressure from Ruen, Satsuki took on the request to find the Heliotrope ring without taking it too seriously.
From that day the demon and human would start working together.
Since meeting Ruen, No, More like since finding that ring, It seems like the world has been swallowed by a dream.