Ningyo no Awakoi

Asana Amamizu's family has treated her like a monster ever since a mysterious red mark appeared on her wrist. Now sixteen years old, she attends the Yotsura Girls Academy, and all the students are chattering excitedly about the new language arts teacher, the handsome Sakuya Shigure. Asana, however, keeps her distance. That is until one day, when an unexpected marriage proposal falls right in her lap. Thus begins a romantic fantasy in the imperial city!

(Source: Yen Press)