Tada Shizuka ni Kiesaru Tsumori deshita

Leticia, the daughter of a count, falls in love with her childhood friend, Severan. She thinks that she and her beloved will one day marry... until her step-sister shows up. Within two months of her mother's death, her father takes in a lover and her daughter, and Leticia quickly finds herself without a place to call her own. And then, with Severan as well... So she thought she might as well just quietly disappear... or so she thought!?

(Source: Kodansha, translated)