Fuminori Teshima 
An Archdemon’s Dilemma: How to Love Your Elf Bride (Manga) Volume 6 [EPUB ebook] 

Following the attack in Kianoides by a sorcerer who looks just like her, Nephy returns to the castle, armed with an invitation to a ball hosted by Archdemon Bifrons.

Though reluctant to attend, Zagan accepts and decides to get everyone dressed up for the occasion. But what good could come from getting involved? Meanwhile, Nephy remains troubled over whether or not to tell Zagan of her mysterious assailant.