An Archdemon's Dilemma: How to Love Your Elf Bride: Volume 19 by Fuminori Teshima

After enjoying a sightseeing trip with his companions, proposing to Nephy, and just generally taking a nice long break, Zagan finally reaches the ends of the earth.

With all thirteen Archdemons present, Eldest Marchosias reveals the shocking truth behind the war from one thousand years ago. Also, in one year, the world will apparently end. Before Zagan can carefully process this continuous stream of revelations, Eldest Marchosias’s schemes are already set in motion!