How NOT to Summon a Demon Lord (Manga) Vol. 24 by Yukiya Murasaki, Naoto Fukuda

The war is over, and peace finally reigns--but an even greater conflict looms on the horizon. Our mighty Demon Lord faces an entirely new kind of trouble after he gives one ring to Rem and another to Shera. The rings are a matching pair...wedding rings, to be precise. Rem and Shera have just been wed to each other without their knowledge! Diablo must now scramble to untangle this mess before the ladies discover the truth!