Dungeon Builder: The Demon King's Labyrinth is a Modern City! (Manga) Vol. 4

The war rages on! Outnumbered, Procel splits his main force and goes on the offensive...but will it be enough? A nightmarishly powerful monster awaits Quina and Rorono in the dungeon of the Demon Lord of Mucus. Meanwhile, a certain Ancient Elf is trapped in the labyrinth of the Demon Lord of Chaos...or is the Demon Lord trapped with her?