Seijo no Migawari to Shite Yatte Kita Fiancée-dono no Yousu ga Okashii

As the country's top court magician, the strong and handsome Oswald attracts attention from those around him. However, one day, while protecting his fiancée, the saint, from a magical beast, he is injured and loses both his good looks and magical powers. The saint then informs him that she has unilaterally broken off their engagement and is offering her younger sister, Chelsea, as his new fiancée. Chelsea devotes herself to Oswald, but there are rumors that she is being oppressed by the saint and that she harbors a secret... This is a love fantasy about a court magician and a troubled young lady. (Source: Natalie, translated)