Dekiai no Kusari - Daifuugou to Kawareta Reijou

Marion, the daughter of a marquis, struggles to find a marriage partner due to her gambling father's bad reputation. After her father suddenly dies, she and her sickly mother are left with enormous debts and are forced out of their home. Desperate to protect her mother, Marion begs the wealthy creditor Dean for more time to repay the debt. Instead, he offers her a condition: she must become his mistress. Though she initially resents the forceful Dean, she gradually finds herself drawn to the kindness he occasionally shows, leading to a passionate and complicated romance. Original Webtoon