Ouji-sama wa Inma no Torikaekko deshita Teishuku na Reijou wo Dame ni Suru Nyoro no Yuuwaku

Leticia, a plain and uptight young lady from a fallen noble family, is growing increasingly anxious as she reaches marriageable age but still hasn't found a husband. She has a childhood friend named Ethelbert, a prince and a handsome, popular man who constantly changes girlfriends. While she resents Ethelbert for giving her love advice every time they meet, she finds herself strangely drawn to him, yet she's convinced that she and Ethelbert are destined never to be together…!? Can this uptight young lady resist the prince's seductive charm!?

(Source: Shueisha, translated)