Imo Kusa Reijou desu ga Akuyaku Reisoku wo Tasuketara Kiniiraremashita

"Lady Bumpkin"—that is what most of high society called Agnes Evantail, eldest daughter of the venerable House of Evantail. Ridiculed for her outdated makeup and antiquated clothing, she has been a pariah among her peers for as long as she can remember. After yet another failed attempt at becoming engaged, her parents make her attend the princess's engagement celebration in hopes of finding a fiancé there. Agnes begrudgingly goes to the party, where she encounters perfect Nazelbart Florescruz, the princess's fiancé, and the only person to ever show her kindness. When the princess schemes against him and he's branded a villain, it's Agnes's turn to offer him a helping hand. The two are then bound together in the most unlikely turn of events—how will their story unfold? (Source: J-Novel Club)