Oukyuu wo Tsuihousareta Seijo desu ga, Jitsu wa Honmono no Akujo wa Imouto da to Kidzuite mo Mou Osoi - Watashi wa Kachi wo Mitomete Kureru Koushaku to Shiawase ni narimasu

Saint Clarice is suddenly told by the prince she loves that she is no longer engaged to him, and that her own sister, Lisha, is his new fiancée. Furthermore, the prince orders Clarice to marry the Duke of Alt, who is famous for his ugly face.

When she visits the Duchy of Alt by royal order, she meets the Duke, who has a hideous appearance that takes her breath away. The Duke had led an unhappy life because of his face, and even his heart had become desolate. However, when he met the kind-hearted Clarice, he regained his natural warmth.

The two begin to be attracted to each other, and the new life they lead together is...