"Kuji" kara Hajimaru Konyaku Seikatsu: Gensei Naru Chuusen no Kekka, Warawanai Jiki Koushaku-sama no Konyakusha ni Tousen shimashita

Belle, the only daughter of a poor aristocrat, receives an invitation to a ball to be held by the Duke of Rouvent. She arrives at the house dressed to the nines, only to be summoned by the duke's butler. She's dressed up in all her finery, but what she's told is that she's betrothed to the next duke, Mr. Allen...!

"I'm just an invited 'mob' daughter, and I'm the fiancée of the next duke, whom I've never even met...?"

(Source: Live Comics, translated)