Ikiokure Seijo no Shiawase

"Well, what do you expect? You're twenty-seven years old now." Saint Marialite can't believe her ears when her fiancé, the crown prince, breaks off their engagement due to her age. She doesn't let that get her down, though; considering the hardship she has endured over the past few years, her mental fortitude allows her to calmly accept the prince's decision and return home. However, when she gets there, she finds...a boy with horns?! The demon prince grows at an unbelievable speed, and in no time at all, he falls head over heels in love with Marialite. Now, he's determined to bring her back to his own country! What might bloom between the easygoing saint and the naïve demon prince in this romantic fantasy? (Source: Cross Infinite World)