Fuminori Teshima 
An Archdemon’s Dilemma: How to Love Your Elf Bride (Manga) Volume 10 [EPUB ebook] 

The culprit behind Nephy’s transformation into a little girl reveals herself. It’s none other than one of the Archdemons, Orias. Faced with this master of celestial mysticism, Zagan tests out his new power.

Can he defeat another Archdemon? And why exactly has Orias done this? What is her secret? All is revealed in this volume of An Archdemon’s Dilemma: How to Love Your Elf Bride.