Marielle Clarac's Engagement

Marielle Clarac's Engagement summary:

Plain and inconspicuous, she was high society's unattractive wallflower. Even so, Marielle was proposed to. Moreover, her fiance is Simeon-sama, the popular knight of the Imperial Guard! Why is he with someone like her? No matter how much she was envied and scorned, Marielle was happy. Well, because his appearance was that of a calm, black-bellied Adonis!