Amemiya Nagisa, who is in love with Noin, a villainous marquis who appears in a novel, is destined for death... but she is reincarnated as his younger sister, Frau!? In this world, even if they are not related by blood, love between siblings is forbidden. In order to prevent anyone from taking over her beloved Noin, she will "break all the love flags" as the "villainous lady, Frau!"