ookami shoujo to kuro ouji [Manga]
Erika lied to her friends about having a boyfriend by showing a picture of an anonymous guy who turned out to be a a schoolmate of hers and was shortly recognized by her friends. Their conversations then was overheard by the guy, Sata Kyouya. Erika went to explain and proposed her idea of faking as lovers. However, Sata who gave off the nice-charming feelings guy turns out to be a black prince and used her reasons to blackmail her instead.