Mujikaku Seijo wa Kyou mo Muishiki ni Chikara wo Tare Nagasu

Overshadowed by her saintly sister Flora, plain Carolina seizes a chance to be useful by agreeing to political marriage with a prince rumored to be cruel. But the prince is nothing as expected—he’s a gentleman, and Carolina feels valued for once in her life. As Carolina blossoms, she discovers a sense of self-worth and a mysterious power, while Flora’s perfect life back home starts to crumble.

(Source: Crunchyroll)