Majime-kei Tennen Reijou wa Toshishita Ouji no Omoi ni Kizukanai

Garnet Frazier, daughter of Marquess Frazier, has her engagement broken off by the first prince for selfish reasons. Furthermore, she was ordered to be engaged to the second prince Razulis, who was rumored to be in poor health and confined to his detached palace. Garnet, worried about the future of her country, decides to place Razulis on the throne, but...

(Source: Micro Magazine-sha, translated)