Sora Yume

On the day her parents leave for a business trip, Satsuki Morinaga finds a sparkling yellow ring in her house. When she puts it on, a demon named Ruen Egrandin is released from inside it. He asks — semi-forcefully — for her help in finding another ring called the Heliotrope, which was sealed inside a different ring. He warns that anyone who puts on the Heliotrope will quickly lose their mind, though simply possessing it causes no harm. In exchange for finding it, he offers to grant a wish. From that day, the demon and the ordinary high school student work together through a world that has started to feel like a dream.