Tenshi ni Kiss

With a family that owns a jewelry business, a high schooler called Ange was named after the world’s largest pink diamond. At a glamorous party where ‘Ange’ is being displayed, she is told by a mysterious woman that although ‘Ange’ is beautiful, it carries a deadly curse. The next day, she visits the diamond again to find that the real ‘Ange’ has been stolen!
(Source: Manga Updates)