Yumemi Satou is a Japanese high school student whose life takes a supernatural turn during a visit to her classmate Seiki's house. While handling a mysterious box there, a football suddenly shatters a nearby window. The impact causes the box to open, releasing a cursed earring that affixes itself to her ear, impossible to remove. This earring subjects Yumemi to a transformative curse: exposure to moonlight or experiencing intense emotions, like a fluttering heart, triggers her metamorphosis into a wild animal. Seeking a solution, she journeys to Germany, where she learns the earring harbors the spirit of an evil prince. Yumemi has brown hair, brown eyes, and is often depicted wearing hair ribbons.