Original Webtoon:
Comico, ComicFesta

Official Translations:
English: Coolmic, Renta, Pocket Comics, MangaPlaza

A poor commoner, Sophia, who works at a prostitute house. Her only relative, sister, is expecting Sophia's smartness and takes guests at Sofia's expense without selling her body.
But one day, her sister fell ill and Sophia decided to take her guests instead. It was the renowned Crown Prince Hugo, who was the executor of justice.
Sofia decides to approach Hugo to get her sister recuperate in the castle. That body is the only one I can give. Hugo, who is strict and does not attract others, does not give back. Actually, Sofia is also the necessary person for Hugo...?