The Bubble Love of the Mermaid, Vol. 1 (light novel) — Akumi Agitogi

A tragic mermaid’s tale deserves a romantic, happy ending! Asana Amamizu’s life changed forever when a red, scale—like mark appeared on her wrist. Ever since, her family has treated her like she’s a monster. Now sixteen years old, she does her best to live normally and attends the Yotsuru Girls’ Academy. One day, the school is suddenly abuzz with exciting news: the handsome new Language Arts teacher, Sakuya Shigure, has arrived. Unlike the other girls, Asana keeps her distance. After all, a guy like that wouldn’t have anything to do with a girl like her. That is, until an unexpected marriage proposal falls right into her lap! She and Sakuya may have more in common than she could have imagined.