Jiyuu Kimamana Seirei-hime

Olivia, the only daughter of the Cypherd family, is a strange girl who never showed any emotions. Even her own father is fearful of her, and her mother, the only person who ever loved her, died when she was 10 years old. After that, her stepmother and stepsisters mistreated her and imprisoned her in the attic, until by chance she regains memories of her previous life and decides to escape. In doing so, she sends an SOS message to Sirius, a boy who used to treat her kindly like an older brother, which will eventually lead to a major incident in their country. This is the story of a girl's disappearance, and a very rich man's doting of that girl, even while the country is falling apart.

(Source: Kodansha, translated)