Atomawashi Reijou wa, Koutei Ichizoku no Aisare Sewagakari ni Narimashita

Her family always put her brother first. Her fiancé always put his best friend first. However, after Sylvia has been looked down on just for expressing her desires her entire life and too many betrayals from her fiancé to count, she decides enough is enough. She declares that she's done being everyone's afterthought and is going to prioritize herself from now on. That very day, a split-second judgment to rescue a young street urchin turns out to be a decision that will change her life. She quickly realizes that the young boy is actually the emperor's illegitimate child Leon, and her own talents are soon discovered by the emperor's half-brother, the "Battle-Crazed Duke", Wilhart. Wilhart asks Sylvia to be Leon's attendant in the Imperial Palace, and for the first time in her life, she feels needed. And despite the rumors of Wilhart's cold, war-hardened demeanor, Sylvia finds him gazing at her with a passion he's never shown anyone else...! (Source: MangaPlaza)