Higeki no Heroine Buru Imouto no Sei de Konyaku Haki shita no desu ga, Nazeka Seigikan no Tsuyoi Outaishi ni Karamareru You ni Narimashita

Leia's life is turned upside down after her younger sister claims she's a cruel villain. Leia's fiancé breaks off their engagement, leaving her no choice but to throw herself into her saintly duties. But when confronted by the righteous Crown Prince Eric, she finds herself under his scrutiny. He's determined to suss out her true nature, but why does it involve living in the palace with him?!

(Source: Seven Seas Entertainment)