Fuminori Teshima 
An Archdemon’s Dilemma: How to Love Your Elf Bride (Manga) Volume 9 [EPUB ebook] 

Zagan’s group travels to Nephy’s old home, the hidden elven village in the northern holy lands, to learn the secrets of the high elves. Upon their arrival, however, they get trapped in a time-distorting barrier and Nephy gets transformed into an adorable little girl. Who would do such a thing?! And exactly what is their objective?!

Zagan is unsure what to do, as Nephy has reverted to a time from before she knew suffering. He’s forced to ask himself—does he have any right to restore her when she’d be happier living inside the barrier as an innocent child forever?