Asana Amamizu’s life changed forever when a mysterious red mark, resembling a fish scale, appeared on her wrist. Since that day, her own family has treated her like a monster, leaving her isolated and shunned. Now sixteen years old, she attends the all-girls Yotsuru Girls Academy in the imperial city, doing her best to live a normal life despite the cold treatment she receives at home. When the handsome new language arts teacher, Sakuya Shigure, arrives on campus, the entire school is abuzz with excitement. Unlike her classmates, Asana keeps her distance, believing a boy like him would never be interested in someone like her. However, her world is turned upside down when Sakuya unexpectedly presents her with a marriage proposal. This sudden offer hints that they may have far more in common than she could have ever imagined, launching a romantic fantasy where a tragic mermaid-like girl might finally find a happy ending.