Nise Seijo no Imouto ni Subete wo Ubawareta Watashi ga Hontou no Seijo deshita

Adiyah was born as the next Holy Maiden of Awakening, inheriting the power to banish demons known as Dream Thieves. However, her younger sister conspires with a Dream Thief to steal those powers, leaving Adiyah to be disparaged as "the impotent holy maiden." Caught in her sister's cunning trap, she is terrorized by her peers and family alike, cast aside by her fiancé, and left with nothing. After years of this torment, she reunites with a boy she saved in a dream world when she was young... and he turns out to be an imperial prince?! (Source: MangaPlaza)