"On that night, I became the cursed monster's bride—"

Stella, the eldest daughter of the Viscount Quinwitch, though she was adopted, lived happily with her kind family. However, one day, Stella's younger sister Lilinette was chosen as the "Monster's Bride". Once a century, a cursed monster confined to a castle requires a sacrifice, so Stella resolves to go there in place of Lilinette. And there, she meets the monster - a bloodstained vampire named Lavi.