Sora Yume Portable

Satsuki is spending her last week of summer vacation alone while her parents travel. She finds a glowing yellow ring — the Chrysoberyl — and puts it on, releasing the demon sealed inside: Ruen Egrandin, who needs her help locating another ring called the Heliotrope. He warns her: putting on the Heliotrope guarantees madness. Finding it without wearing it is the only task. Satsuki agrees without thinking too carefully, and a reluctant partnership between a demon and a high school girl begins.