Ouji ga Kuuki Yomana Sugiru

Tormented by her stepmother and stepsister, marquis's daughter Natalie Lennox is at her breaking point during a pre-debut ball at age nine. She is suddenly rescued by the second prince, Mikhail Liradovia, whose direct speech shocks the nobles present and earns him a reputation for being "unable to read the room." From that day, Natalie's fate changes drastically. Though she tries to keep her distance, the prince's unorthodox actions constantly pull her in—eventually leading him to propose marriage! https://manga-one.com/manga/27620/chapter/328571